2 Basic Limnology 2.1 INTRODUCTION Lake managers, students, consultants, and others interested in lake and reservoir restoration should have a thorough understanding of limnology. The next two chapters outline some basic principles of limnology that are significant to restoration and management decisions. A brief comparison of lakes and reservoirs is presented in this chapter, along with a description of regional lake conditions and the forces, both external and internal, that promote lake and reservoir problems. Procedures to obtain the data necessary to diagnose lake condition, select a restoration alternative, and prepare a project report are described in the next chapter. Readers familiar with the fundamentals of limnology could go directly to sections on restoration methods. While these next two chapters cannot substitute for the in-depth understanding of lim- nology required to make competent and effective decisions, they do provide a review or guide to some basic principles. The reader is referred to Hutchinson (1957, 1967, 1975), Cole (1994), Horne and Goldman (1994), Lampert and Sommer (1997) and Scheffer (1998) for thorough discussions of limnology. Welch and Jacoby (2004), Wetzel (2001), and Kalff (2002) are especially useful for their holistic viewpoints, and for their coverage of macrophyte biology and stream and reservoir ecology. 2.2 LAKES AND RESERVOIRS The physics, chemistry, and biology of dimictic (deeper lakes that thermally stratify in summer and winter) natural lakes have dominated limnological literature and the training of many limnol- ogists. This bias reflects the fact that there are many of these lakes in North America and Europe. It is also a result of the emergence of “limnology schools” located primarily in North American and European areas dominated by deep lakes. But, shallow lakes are far more common than deep lakes (Wetzel, 1992), and limnology programs emphasizing them are now emerging, particularly in Europe. Reservoirs are as important as natural lakes for recreation, but have additional values for flood control, hydropower generation, and water supply. While both lakes and reservoirs are subject to silt, organic, and nutrient loadings, reservoirs are more likely to have water quality problems due to their usually large watersheds and their morphometric configurations. Reservoirs are a vital part of the economy of many nations. The U.S. Army Corps of Engineers (USCOE) manages approx- imately 783 reservoirs with a combined surface area of 27,000 km 2 (Kennedy and Gaugush, 1988). Despite their abundance and importance, most limnology texts only mention them, or incorrectly imply that they are functionally equivalent to natural lakes and that no distinction is necessary. While natural lakes and reservoirs have biotic and abiotic processes in common, they have important differences. Both have similar habitats (pelagic, benthic, profundal, and littoral zones), organisms, and processes, but it is their differences, summarized by Thornton et al. (1980), Walker (1981), Kennedy et al. (1982, 1985), Søballe and Kimmel (1987), Thornton et al. (1990), and Kennedy (1999, 2001) (Table 2.1), that also must be understood to successfully manage them. These fundamental reports are important supplements to most texts in limnology. A brief compar- ison of lakes and reservoirs is presented here. Copyright © 2005 by Taylor & Francis Reservoirs differ from lakes in their geologic history and setting, basin morphology, and hydrologic factors (Kennedy et al., 1985; Kennedy, 2001). When natural lakes and USCOE reser- voirs are compared, it is apparent that reservoirs are located primarily where flooding may occur or where water shortages require water storage. Reservoirs thus dominate the middle latitudes of the U.S. (Walker, 1981). Reservoirs are also used for hydropower generation. Very small reservoirs for recreation and farming operations are found at all latitudes. Lakes of North America are also located in distinct regions. They are: (1) the continental glacial lakes in the mesic northeast, Canada and upper midwest, (2) the mostly alpine glacial lakes in Alaska and the mountainous west, (3) the coastal plain and karst (solution) lakes of the southeast, especially Florida, and (4) scattered small regions of playas, potholes and sandhill lakes in arid and semi arid areas (J.M. Omernik, USEPA, personal communication). Further discussions of these lake distributions are found in Hutchinson (1957) and Frey (1966). Latitudinal differences in climate and geology have a major influence on the quality and rates of materials loaded to lakes and reservoirs, and on their degree of thermal stratification and mixing. The average reservoir watershed area is nearly an order of magnitude greater than the average lake’s watershed, a factor accounting for the much higher average areal water (and contaminant) loadings to reservoirs (Table 2.1). Some lakes also have large watersheds and thus, like reservoirs, have high water loads. Reservoirs can become distinctly “lake-like“ during summer low flow periods. Therefore, it should be noted that the values in Table 2.1 are averages, and that the ranges of lake and reservoir characteristics overlap. Natural lakes are more likely to be located centrally in a fairly symmetrical drainage area, whereas reservoirs are elongated and dendritic, and usually at the downstream boundary of the watershed. The deep zone of a reservoir is normally at the dam; in lakes there may be several “deep holes.” Average nutrient and sediment loads are much higher for reservoirs and this material may have undergone a far longer period of in-stream processing than material loaded to natural lakes. Water often enters lakes via smaller streams that are likely to traverse wetland or littoral areas, whereas reservoirs may have characteristics of a river for long distances into the reservoir. While natural lake outflows are at the surface, or occasionally through the ground, reservoirs usually have multiple depth, constructed outlets, leading to in-reservoir mixing processes and to discharge of water that might be anoxic, enriched with soluble nutrients, or high in hydrogen sulfide, TABLE 2.1 Comparison of Geometric Means (Probability That Means for Each Comparison Are < 0.0001) of Selected Variables of Natural Lakes and Army Corps of Engineers Reservoirs Variable Natural Lakes (N = 309) Reservoirs (N = 107) Drainage area (km 2 ) 222.00 3228.00 Surface area (km 2 ) 5.60 34.50 Maximum depth (m) 10.70 19.80 Mean depth (m) 4.50 6.90 Hydraulic residence time (yr) 0.74 0.37 Areal water load (m/yr) 6.50 19.00 Drainage/surface area 33.00 93.00 P loading (gm/m 2 /yr) 0.87 1.70 N loading (gm/m 2 /yr) 18.00 28.00 Source: Modified from Thornton, K.W. et al., 1980. Symposium on Surface Water Impoundments. Proceedings Am. Soc. Civil Eng. pp. 654–661. With permission. Copyright © 2005 by Taylor & Francis methane, and reduced metals. Lake levels vary with precipitation, evaporation, and surface outflows, but it is uncommon for the amplitude to be large or to change quickly. An exception is the wind- induced displacement of some of the water mass, creating a to and fro “sloshing” of water in the lake basin, sometimes with amplitudes of one meter or more (surface and internal seiches). A well- known example is the occasional seiche in Lake Erie (U.S Canada). Reservoirs, however, can have rapid and significant changes in levels due to management decisions and these changes in level may eliminate or greatly reduce the littoral community of rooted aquatic plants. Unlike lakes, reservoirs are operated to store and release water, and these operations profoundly influence their limnological characteristics (Kennedy, 2001; Cooke and Kennedy, 2001). For exam- ple, when deep waters are released, heat is stored. When surface waters are released heat is dissipated. These actions greatly alter thermal structure, including depth of the metalimnion (layer of water with a sharp thermal gradient) and retention or loss of materials. Lakes and reservoirs represent a continuum of ecological conditions (Canfield and Bachmann, 1981). Kimmel and Groeger (1984) and Søballe and Kimmel (1987) viewed this continuum as one ordered by water residence time (volume divided by outflow rate), and indicated that reservoirs and natural lakes with similar residence times have similar ecological attributes. In rapidly flushed systems, for example, algal abundance is less likely to depend on nutrient concentrations than on flushing rate (Chapter 6). Therefore, despite features that might separate lakes and reservoirs as classes of aquatic habitats, convergence can occur when water residence times are similar. Geographic location of a reservoir determines the quantity and timing of inflow. For example, inflows in some areas of California are in spring to mid-summer, whereas peak inflows in the Pacific Northwest and southeastern U.S. are in winter to early spring. Similarities and differences between lakes and reservoirs based on water residence times are thus modified by location (Kennedy, 1999). Figure 2.1 illustrates the expected gradient in reservoir characteristics of a main-stem reservoir (dam on the stream) from the river entrance to the dam. Unlike many natural lakes where water enters from several smaller tributaries draining comparatively small sub-watersheds, reservoirs have a distinct riverine zone dominated by flow and mixing, followed by a transition zone where inflow velocity slows, rapid sedimentation begins, and water clarity increases. When inflowing river water is colder than surface water of the reservoir, a “plunge point” is found where the colder, heavier water loses velocity and descends to a depth equal to its density, creating a distinct inter- or underflow (Figure 2.2). Unlike lakes, where it is often assumed that nutrient loads are completely mixed with lake waters, loading to a reservoir might not mix with upper waters at all, but instead might be carried through the reservoir via an inter- or underflow, greatly altering standard loading model assumptions (Chapter 3) (Kimmel and Groeger, 1984; Gaugush, 1986; Walker, 1987). The lacustrine zone near the dam is the most lake-like, with thermal stratification and a higher probability that algae growth is nutrient limited. Some natural lakes in narrow valleys, with large inflow rivers and low water residence times, have many reservoir characteristics. This gradient of conditions along the length of a reservoir means that reservoir characterization requires multiple sampling stations. The same is true for large natural lakes, and lakes with distinct pelagic and littoral zones. Reservoir basin design also influences hydrodynamic features. For example, a tributary reservoir and a main stem reservoir receiving identical water loads and having identical basin volumes are likely to have different responses. Main stem reservoirs have low capacity to store excess volume and thus have water residence times that fluctuate with water loading events, whereas tributary reservoirs have much higher storage capacity and are used for flood control. In these reservoirs, the hypolimnion may be large whereas the main stem reservoir may be longer and shallower and greatly influenced by interactions between sediments and overlying water (Kennedy, 1999). Reservoirs are important sources of fresh water for potable, irrigation, and industrial purposes. Their protection and management requires that more traditional views of sampling, correlations between loading and responses of biota, and choice of restoration techniques be modified to take these, and the basic differences between natural lakes and reservoirs, into account. Copyright © 2005 by Taylor & Francis 2.3 BASIC LIMNOLOGY 2.3.1 P HYSICAL–CHEMICAL LIMNOLOGY Some lakes and reservoirs stratify thermally during summer months into an upper warm, well- mixed zone termed the epilimnion. Below this is a zone of rapidly decreasing temperature with depth, the metalimnion, followed by a deep, colder, often dark bottom layer, the hypolimnion. This phenomenon, brought about by wind mixing, solar input, and by large differences in water density between cold and warm waters, is a primary determinant of summer physical, chemical, and biological interactions. During ice cover lake water temperature inversely stratifies, with colder water at the surface. This happens because water’s maximum density is at 4°C, and water colder than this temperature, including ice, is lighter and floats above this slightly warmer layer. Lakes with two mixing periods (spring and fall) and two stratified periods (summer, winter) are dimictic and are typical of deep lakes and reservoirs of north temperate latitudes (Wetzel, 2001). Details of mechanisms leading to this and other types of thermal stratification are found in all basic limnology texts. Figure 2.3 illustrates the characteristics of the three thermal layers in a dimictic lake, or in the lacustrine zone (Figure 2.1) of a reservoir during summer months. The figure also illustrates typical summer temperature and dissolved oxygen (DO) profiles with depth in a stratified eutrophic lake or reservoir. Polymictic lakes are more common than dimictic lakes. Because polymictic lakes are shallow, they may mix continuously, or stratify briefly (hours, days) in calm, hot weather, followed by renewed complete mixing. Polymictic lakes are found at all latitudes. FIGURE 2.1 Longitudinal zonation in environmental factors that control primary productivity, phytoplankton biomass, and trophic state within reservoir basins. Changes in shading indicate decline in turbidity. (From Kimmel, B.C. and A.W. Groeger, 1984. Lake and Reservoir Management. USEPA 440/5-84-001. pp. 277–281. Riverine zone Transitional zone • Broader, deeper basin Lacustrine zone • Broad, deep, lake-like• Narrow basin • High flow • High susp. solids, low light • High nutrients, advective supply • Light limited photosynthesis • Algal cell loss by sedimentation • Organic matter supply allochthonous • More “eutrophic” • Reduced flow • Lower susp. solids, more light • Advective nutrient supply reduced • High photosynthesis • Algal cell loss by sedimentation, grazing • Intermediate • Little flow • Clearer • Internal nutrient recycling, low nutrients • Nutrient limited Photosynthesis • Algal cell loss by grazing • Organic matter supply autochthonous • More “oligotrophic” Copyright © 2005 by Taylor & Francis There can be significant modifications of temperature regimes, particularly in reservoirs. River inflows to reservoirs may have very different temperatures than reservoir waters, producing under- inter-, or overflows of incoming water (Figure 2.2). The upper reaches of the reservoir, like the wave washed littoral zone of a lake, may exhibit little thermal stratification except during hot, calm, low-flow periods. In the transition zone (Figure 2.1), where mixing and sedimentation processes are dominant, the volume of a reservoir’s hypolimnion may be small. Only in the deep lacustrine zone is the temperature stratification similar to natural lakes, though the hypolimnion is likely to be less stable due to underflows and withdrawals of deep water at the dam. The shape of a reservoir or lake’s basin affects its productivity, kinds of organisms, water chemistry, and the choices available to manage and restore it. Most natural lakes are small in area and shallow (mean depth ≤ 3 m). Rooted plants, and algae associated with leaf and sediment surfaces, can have very high primary productivity, biomass, and areal distribution, unless the lake is turbid from silt loading, wind mixing, or algal blooms that cause rooted plants to be light-limited. Also, as noted in later sections and other chapters, the large area of shallow, warm sediments and the small hypolimnetic volumes associated with (mainly) polymictic shallow lakes and reservoirs provide ideal circumstances for processes that allow sediment nutrient release (actually recycling or “internal loading”) and transport to the water column. This can greatly stimulate algal produc- tivity. Internal loading processes may be biological (e.g., microbial activities and temporary anoxia, and sediment disturbance by methane release or by burrowing animals), chemical (e.g., high pH from photosynthesis), and physical (e.g., turbulence from the wind) in nature (Chapter 3). Because of these processes, lake productivity is often negatively correlated with mean depth (Wetzel, 2001) and with the ratio of mean to maximum depth (Carpenter, 1983). Therefore, many shallow water bodies will have more algae or rooted plants than the less common steep-sided, deep lakes and reservoirs. High macrophyte growth is to be expected in shallow lakes. A hypsograph (a representation describing the relationship between lake area and depth) is useful in explaining this. Figure 2.4 compares the area–depth relationship for two hypothetical lakes with different areas of shallow FIGURE 2.2 Density flows in reservoirs. The upper panel illustrates an “overflow“ of warm incoming waters, the middle panel illustrates an “interflow,“ and the bottom panel shows an “underflow.“ (From Moore, L. and K. Thornton (Eds.). 1988. Lake and Reservoir Restoration Guidance Manual. USEPA 440/5-88-002. Dam Outflow Dam Outflow Dam Outflow Inflow Inflow Inflow Overflow Interflow Plunge point Plunge point Underflow Copyright © 2005 by Taylor & Francis water. Both lakes could have nuisance algal blooms if nutrient concentrations were high. Only the shallow one has the potential to have a large area with rooted plants because of the extensive shallow, well-lighted sediment area. Physical factors, particularly waves, transparency, and the slope of the littoral zone (amount of stable sediment area exposed to light) are among the determinants of maximum macrophyte biomass and maximum depth of plant colonization (Canfield et al., 1985; Duarte and Kalff, 1986, 1988) (Chapter 11). The development of a hypsograph is an important first step in lake and reservoir problem diagnosis. 2.4 BIOLOGICAL LIMNOLOGY Lakes and reservoirs have three distinct and interacting biotic communities (Figure 2.5): (1) the wetland-littoral zone, and its sediments, (2) the open water pelagic zone, and (3) the benthic or deep water (profundal) zone and sediments. Problems or characteristics appearing in one zone (e.g., deep water oxygen depletions, littoral zone aquatic plants, pelagic zone algal blooms) directly or indirectly affect other zones, meaning that successful lake restoration requires a holistic view of lake and watershed processes. For example, nutrients causing algal blooms may come from lake sediments and decomposition of littoral plants, as well as from external loading. All sources might require attention to solve the problem. FIGURE 2.3 Cross section of a thermally stratified reservoir indicating location and characteristics of the epilimnion, metalimnion, and hypolimnion, and typical summer temperature-dissolved oxygen distributions in the lacustrine zone of a eutrophic reservoir. (From Gunnison, D. and J.M. Brannon. 1981. Characterization of Anaerobic Chemical Processes in Reservoirs: Problem Description and Conceptual Model Formulation. Tech. Rept. E-81-6. U.S. Army Corps Engineers, Vicksburg, MS. * * Atmospheric aeration Epilimnion Metalimnion Hypolimnion Sediment – region of material adsorption and release • Warm isothermic • Abundant oxygen • Warmwater fishery • Warm to cold thermal discontinuity • Variable oxygen • Mixed fishery • Cold isothermic • Oxygen low or absent-increased concentration s of soluble forms of contaminants and nutrients • Coldwater fishery if oxygen adequate * Typical vertical temperature and do distributions during stratification: Bottom Hypolimnion Metalimnion Epilimnion Temperature DO Copyright © 2005 by Taylor & Francis Rooted emergent, floating, and submersed vascular plants, collectively called macrophytes, and their attached flora and fauna, dominate the wetland-littoral. These plants are distinctly different from the microscopic, floating (planktonic) cells, colonies, and filaments of algae, often seen as surface “scums” in some eutrophic systems. Macrophytes are usually vascular plants and are found in shallow water. They may have large masses of filamentous (string or hair-like) algae attached to them as thick mats. Shallow, lighted sediments often have a highly productive epilithic, epipelic, and epiphytic flora (algae growing on surfaces of rocks, sediments and vascular plants). Macrophyte biology is described in Chapter 11. The littoral zone often has high species diversity, and is commonly the site where fish repro- duction and development occurs. It is also an important waterfowl habitat. Littoral zone plant FIGURE 2.4 Depth-area hypsographs. Solid line illustrates the less common deep lake with a small littoral zone; dotted line illustrates the more common shallow lake with extensive littoral area and volume. (From Cooke, G.D., E.B. Welch, S.A. Petersen, and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, 2nd Edition. Lewis Publishers and CRC Press, Boca Raton, FL. FIGURE 2.5 Biotic communities in lakes and reservoirs.(From Cooke, G.D., E.B. Welch, S.A. Petersen, and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, 2nd Edition. Lewis Publishers and CRC Press, Boca Raton, FL.) 150 M 2 x 5 10 15 20 25 050 Area 100 Surf. Depth in meters Wetland-littoral Profundal zone Pelagic Copyright © 2005 by Taylor & Francis biomass replaces itself two or more times per summer in productive lakes, leading to inputs of non-living dissolved and particulate organic matter, termed “detritus,” to the water column and sediments. Detritus, whether from watershed drainage or from in-lake productivity, is a stable energy and nutrient source to the lake’s food webs, especially to microbial flora and plankton (Wetzel, 1992, 1995). Many lakes, especially those surrounded by dense forest, are actually het- erotrophic (photosynthetic rate is less than total respiration rate), and depend upon organic carbon from terrestrial sources to subsidize their food webs (Cole, 1999). Therefore lakes are strongly linked to the land, not only through nutrient and silt loading, but through detritus imports. Macrophytes, in addition to being a significant energy source and habitat, stabilize littoral zone sediments from the impacts of wind and boat-generated waves, thus reducing internal P loading and sediment resuspension (Bachmann et al., 2000; Anthony and Downing, 2003; Horppila and Nurminen, 2003). Macro- and microplankton, and the fish and invertebrates grazing on them, dominate the pelagic zone. The plankton includes algae that produce unsightly “blooms” and low water clarity, and bacteria, fungi, Protozoa, and filter-feeding crustaceans like Bosmina and Daphnia. The pelagic community obtains energy from sunlight and from detritus transported to it from stream inflows and the littoral zone. The plankton of most enriched lakes and reservoirs is dominated by one or a few species of highly adapted algae and bacteria, particularly nuisance blue-green algae (cyano- bacteria). Bosmina, Daphnia, and other planktonic microcrustacea are significant grazers of detritus, bacteria, and some algae species, though their abundance may be regulated by complex interactions with predators such as fish and insects (Chapter 9). The profundal benthic community receives nutrients and energy from organic matter loaded to or produced in the lake or reservoir and deposited on the sediments. Inorganic forms of nutrients may be added to the sediments in the form of precipitates. This pelagic-benthic coupling is a fundamental feature of lakes (Vadeboncoeur et al., 2002). In productive lakes and reservoirs, large areas of the sediment community in deep water are continuously anoxic during thermal stratification due to intense microbial respiration that is stimulated by deposits of detritus. Anoxic conditions provide conditions favoring high rates of nutrient release to the water column (Figure 2.3). 2.5 LIMITING FACTORS Nuisance densities of algae or macrophytes, and associated water quality problems, are conditions managed by manipulating or altering their biomass or by manipulating one or more of the factors controlling their abundance. Macrophyte density, while in part related to sediment type and com- position, and to nutrient factors, is often determined by light availability (Duarte and Kalff, 1986; Canfield et al., 1985; Barko et al., 1986; Smith and Barko, 1990). Long-term control of algal biomass requires significant water column nutrient reduction. Phosphorus (P) is most frequently targeted because it is usually the nutrient in shortest supply relative to demands by algae (the limiting nutrient). Phosphorus does not have a gaseous phase so the atmosphere is not a significant source, unlike nitrogen or carbon. Lake P concentration, therefore, can be lowered significantly by reducing loading from land and in-lake sources. A significant reduction in external nutrient loading is an essential, but not necessarily sufficient, step toward reducing lake P concentrations. Internal loading from aerobic and anaerobic sediments, groundwater seepage, decomposing macrophytes, sediment resuspension, and organism activities might add more nutrients to the lake than external loading during some times of the year. The shape of a lake’s basin (Figure 2.4) has an important bearing on the amount of internal loading. Most of the variance in algal productivity among some Ontario lakes was explained by the ratio of sediment area in contact with the epilimnion to epilimnion volume. Steep-sided, deep lakes have a low ratio, producing less influence on overlying water (Fee, 1979). Epilimnetic sediments are warm, leading to increased microbial decomposition rates and to nutrient release (Jensen and Andersen, 1992). Extensive littoral areas, typical of shallower lakes, may have distinct Copyright © 2005 by Taylor & Francis day-night cycles of high and low DO concentrations that stimulate nighttime P releases, especially under dense macrophyte beds (Frodge et al., 1991). Wind mixing and convective currents may scour sediments or entrain nutrient-rich littoral or bottom waters of shallow lakes, especially those with low macrophyte density, thus transporting nutrients to the pelagic zone. The hypolimnion may or may not be a P source to the epilimnion. When thermal stratification occurs, hypolimnetic waters are isolated from the atmosphere and are usually too deep to permit sufficient light penetration for photosynthetic oxygen generation. Respiration in deep waters leads to DO depletion or elimination, to reducing conditions, and to the associated release of P from sediment iron complexes. High sulfate concentrations may lead to ferrous sulfide (FeS) production under reducing conditions, and loss of Fe control of sediment P (Caraco et al., 1989; Golterman, 1995; Gächter and Müller, 2003). In stratified lakes with low resistance to mixing (large surface area relative to depth), summer winds either briefly destratify the lake (polymixis), or force vertical entrainment of P-rich hypolimnetic water to the epilimnion. In either case, surface water P con- centration increases, stimulating an algal bloom. For example, Stauffer and Lee (1973) calculated that all of the summer algal blooms in Lake Mendota, Wisconsin could be accounted for by transport of P from the metalimnion to the epilimnion. This internal P source to the epilimnion may not be significant in lakes that are deep relative to area of lake surface exposed to wind mixing. This type of lake offers greater resistance to the force of summer wind (Osgood, 1988). The best predictor of vertical P transport to the epilimnion appears to be the vertical gradient of P concentration, not lake morphometry (Mataraza and Cooke, 1997). These ideas are explored in Chapters 3 and 4 with respect to model predictions, and in Chapter 8 where sediment treatment with P inactivating chemicals is discussed. Macroscopic animals play major roles in nutrient releases from lake sediments. Common carp digestive activities release P at rates similar to external loading (La Marra, 1975). Bioturbation (sediment disturbance) by fish and insects and high rates of sloughing of vascular plant tissues are also nutrient sources to the epilimnion. Reviews of internal recycling include Carlton and Wetzel (1988), Marsden (1989), Welch and Cooke (1995), Pettersson (1998), and Søndergaard et al. (2001). These characteristics of littoral and pelagic zones mean that expensive nutrient diversion projects may not meet expectations for reduced algal biomass until internal nutrient sources are addressed (Chapters 4 and 8). Other factors affecting algal biomass include flushing rate, light availability, pH, and zooplank- ton grazing. These factors can be manipulated as part of a management plan, though significant reduction of external and internal nutrient loading remains the central part of plans for long term improvement of excessive algae problems. 2.6 THE EUTROPHICATION PROCESS A eutrophic lake or reservoir is rich in nutrients and organic materials, and those enriched by human activities are said to be culturally eutrophic. We have expanded the definition of the eutrophication process to include the loading of silt and organic matter, as well as nutrients. Thus, we define the eutrophication process as the loading of inorganic and organic dissolved and particulate matter to lakes and reservoirs at rates sufficient to increase the potential for high biological production, decrease basin volume, and deplete DO. This concept of eutrophication is more complete because it includes all materials that produce the eutrophic condition. The eutrophication process and associated major in-lake interactions are summarized in Figure 2.6. Traditionally, eutrophication referred only to nutrient loading, its eventual high concentrations in the water column, and the high productivity and biomass of algae that could occur. Organic matter loading may lead to sediment enrichment and loss of volume. Organic matter, whether added to the water column from external or internal sources, also leads to increased nutrient availability via direct mineralization, or through release from sediments when respiration is stimulated by this organic matter and DO is depleted. Net internal P loading appears to increase exponentially with Copyright © 2005 by Taylor & Francis increasing dissolved organic carbon content of the lake (Ryding, 1985). Allochthonous organic matter contains molecules producing changes in algal and microbial metabolism independently of effects of added nutrients (e.g., Franko and Wetzel, 1981). Finally, organic matter added to a lake or reservoir contains energy that is incorporated, in both dissolved and particulate forms, into plant and animal biomass, leading directly to increased living biomass (the microbial loop). Dissolved and particulate organic matter entering the lake or reservoir from streams, wetlands, and from macrophytes, is of great significance to lake metabolism. These ideas are developed in Wetzel (1995, 2001) and Cole (1999). Silt may be rich in organic matter and in nutrients sorbed to surfaces of particulate matter. These may become available to algae or macrophytes immediately or at some later time. Silt loading also contributes directly to volume loss and to an increase in shallow sediment area. Whether volume loss is produced by silt deposition or by the build-up of refractory organic matter from terrestrial and aquatic sources, the development of shallow areas fosters further spread of macrophytes and their attendant epiphytic algae. Ultimately these plants promote further losses of DO and release of organic molecules and nutrients as they decay (Carpenter, 1980, 1981, 1983) (Figure 2.6). Thus, silt and organic loadings have effects on lakes that are additional to their nutrient content, and cannot be excluded when defining the eutrophication process. This view is not meant to downplay or negate the fundamental importance of high nutrient loading in stimulating lake productivity. Instead, following Odum’s (1971) holistic view, it is meant as a more complete description of the process. Excessive nutrient loading creates potential for eutrophic conditions but does not guarantee increased productivity. Figure 2.6 does not account for the “oligotrophication” effects of high rates of lake flushing and dilution, the effects of organisms in stimulating nutrient release from sediments, or the effects of grazing (or lack of grazing) on algae biomass. Lakes and reservoirs that are naturally eutrophic, or have become so, have characteristics separating them from less enriched and oligotrophic (“poorly nourished”) water bodies. Eutrophic lakes have algal “blooms,” often of monospecific blue-green (cyanobacteria) populations. Some FIGURE 2.6 Loadings and primary interactions in lakes and reservoirs. (From Cooke, G.D., E.B. Welch, S.A. Petersen, and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, 2nd Edition. Lewis Publishers and CRC Press, Boca Raton, FL.) Macrophytes Shallowness, sediment enrichment Nutrients, organic and silt loads Algae Water column nutrients External-internal nutrient load Sediment nutrient release Macroscopic animal grazing Streams, overland flows, wetland discharge Dissolved & particulate organic matter + “microbial loop” Copyright © 2005 by Taylor & Francis [...]... 1 3 4 17 11 9 16 13 6 8 45 52 53 47 44 25 8 6 64 63 71 67 22 66 38 26 67 69 72 39 23 70 40 21 14 61 55 54 27 62 56 57 28 23 60 57 19 23 59 61 17 20 6 50 51 46 19 1 7 58 50 43 18 5 58 42 16 17 17 15 12 1 48 49 17 16 15 65 37 23 36 27 25 23 26 29 68 32 33 24 30 32 35 63 65 74 75 34 31 76 FIGURE 2. 7 Ecoregions of the conterminous United States 1, Coast Range; 2, Puget Lowland; 3, Willamette Valley; 4,... Netherlands pp 27 –38 Kimmel, B.C and A.W Groeger 1984 Factors controlling primary production in lakes and reservoirs: a perspective In: Lake and Reservoir Management USEPA 440/ 5-8 4-0 01 pp 27 7 28 1 LaMarra, V.J., Jr 1975 Digestive activities of carp as a major contributor to the nutrient loading of lakes Verh Int Verein Limnol 19: 24 61 24 68 Lampert, W and U Sommer 1997 Limnoecology The Ecology of Lakes and. .. Kennedy 20 01 Managing drinking water supplies Lake and Reservoir Manage 17: 157–174 Cooke, G.D., P Lombardo and C Brant 20 01 Shallow and deep lakes: Determining successful management options LakeLine (NALMS) 21 : 42 46 Cooke, G.D., E.B Welch, S.A Petersen, and P.R Newroth 1993 Restoration and Management of Lakes and Reservoirs, 2nd Edition Lewis Publishers and CRC Press, Boca Raton, FL Duarte, C.M and J... % % ha ha m mg/L mg/L m kg/yr mg/L kg/km2 /yr km3/yr yr mg/L NCHF 30 34.8 18.0 0.7 6.4 16.4 2. 5 20 .9 4670 364 6.6 33 14 2. 5 1004 183 27 6 6 .2 9.3 148 NLF 8 1.8 3.9 0.0 4.8 66 .2 2.1 20 .9 21 40 318 6.3 21 6 3.5 305 58 96 5.3 5.0 52 NGP WCBP 11 73.0 9 .2 2.0 0.4 0.0 0.6 14.4 24 64 21 8 1.6 156 61 0.6 1943 5666 891 0.9 36 .2 1500 60.6 5.9 1.5 9.9 7.0 1 .2 13.6 756 107 2. 5 98 67 0.9 590 564 551 1.0 4.8 570 Note:... in their characteristics Most lake and reservoir restoration techniques and paradigms were developed from research and testing on less common deep lakes and may not be entirely suitable for shallow lakes Throughout this text, we attempt to emphasize applicability of methods to both classes of lakes Table 2. 2 is a comparison of the characteristics of deep and shallow lakes, primarily based on European... the ecoregions (Figure 2. 12) Final selections of lakes for management or restoration also involve considerations such as intended uses, proximity to users, number of other lakes in the area, and an in-depth analysis of nutrient dynamics in relation to lake trophic state The use of ecoregions for lake management continues to be evaluated A special purpose map of summer total TP in lakes was developed for... Kennedy, R.H and R.F Gaugush, 1988 Assessment of water quality in Corps of Engineers reservoirs Lake and Reservoir Manage 4 (2) : 25 3 26 0 Kennedy, R.H., K.W Thornton and R.C Gunkey 19 82 The establishment of water quality gradients in reservoirs Can Water Res J 7: 71–87 Kennedy, R.H., K.W Thornton and D.E Ford 1985 Characterization of the reservoir ecosystem In: D Gunnison (Ed.), Microbial Processes in Reservoirs. .. Prediction of total phosphorus concentrations, chlorophyll a, and Secchi depths in natural and artificial lakes Can J Fish Aquatic Sci 38: 414– 423 Canfield, D.E Jr., K.A Langeland, S.B Linda and W.T Haller 1985 Relations between water transparency and maximum depth of macrophyte colonization in lakes J Aquatic Plant Manage 23 : 25 28 Caraco, N.F., J.J Cole and G.E Likens 1989 Evidence for sulphate-controlled... and 24 6 U.S Environmental Protection Agency (USEPA) Science Advisory Board 1991 Evaluation of the ecoregion concept Report of the Ecoregions Subcommittee of the Ecological Processes and Effects Committee USEPA-SAB-EPEC-9 1-0 03 Washington, DC U.S Environmental Protection Agency (USEPA) 1998 National strategy for the development of regional nutrient criteria USEPA 822 /R98–0 02, Vadeboncoeur, Y., M.J Vander... Rept E-8 1-9 U.S Army Corps Engineers, Vicksburg, MS Welch, E.B and J.M Jacoby 20 04 Pollutant Effects in Freshwater: Applied Limnology 3rd Edition Spon Press, New York Copyright © 20 05 by Taylor & Francis Welch, E.B and G.D Cooke 1995 Internal phosphorus loading in shallow lakes: Importance and control Lake and Reservoir Manage.11: 27 3 -2 81 Wetzel, R.G 19 92 Gradient-dominated ecosystems: sources and regulatory . 17 16 17 17 16 41 17 16 43 42 46 48 49 51 50 52 53 56 55 70 67 64 60 61 58 58 59 69 71 63 62 67 72 68 65 75 76 65 66 61 57 50 57 45 11 12 13 19 20 19 8 8 18 25 27 44 21 26 14 23 23 22 23 23 24 25 26 30 31 32 33 35 74 36 39 40 54 47 37 38 28 32 29 27 34 23 5 3 4 6 6 6 7 9 17 63 Copyright © 20 05 by Taylor & Francis thus allowing informed management. Petersen, and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, 2nd Edition. Lewis Publishers and CRC Press, Boca Raton, FL. FIGURE 2. 5 Biotic communities in lakes and reservoirs. (From. Welch, S.A. Petersen, and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, 2nd Edition. Lewis Publishers and CRC Press, Boca Raton, FL.) 150 M 2 x 5 10 15 20 25 050 Area 100 Surf. Depth