Changes In Phosphorus Loading Research Articles

Nutrient loading effects on fish habitat quality: Trade‐offs between enhanced production and hypoxia in Lake Erie, North America

Abstract Across diverse systems, nutrient loading from anthropogenic sources into aquatic systems has increased over the past century. Such nutrient inputs may enhance system productivity and thereby increase resource availability but may also lead to undesirable conditions such as hypoxic zones. We examined the habitat quality trade‐offs associated with increases in phosphorus in a model system (Lake Erie, North America) with a history of anthropogenic nutrient loading. Using a water quality model and a bioenergetics growth rate potential model with fine vertical and temporal resolution, we assessed how the quality of habitat for multiple species of adult and juvenile fish changed across a range of phosphorus loading scenarios and across 19 different meteorological years. Increases in phosphorus loading increased invertebrate prey biomass, but also increased the duration and extent of the mid‐summer hypoxic zone. In general, phosphorus loading caused overall habitat quality to decline and only increased peak habitat quality (i.e., spatio‐temporal locations where temperature and prey abundance were already above average), but responses were species‐ and life‐stage specific. One challenge in ascertaining the effects of nutrient loading on fish habitat quality is separating the negative effects of hypoxia from the potential positive effects of increased prey densities. Through various model scenarios, we evaluated the individual effects of hypoxia and increased prey availability on fish habitat quality, demonstrating their potentially counter‐balancing effects. That is, the negative effects of low oxygen on fish habitat quality appear more severe if the prospect that increased hypoxia is accompanied by altered prey densities is not accounted for. Despite modelled responses to altered phosphorus loads, habitat quality responded more strongly to variation in annual meteorological conditions. Annual meteorological conditions such as temperature, vertical mixing, and timing of phosphorus loading had a greater effect on habitat quality for all species and life‐stages than changes in annual amount of phosphorus loading. This limited effect of changes in phosphorus loading on habitat quality probably partially reflects our focus on short‐term (1‐year) changes in loading. Thus, nutrient abatement programmes may not lead to obvious, rapid positive habitat quality responses, as short‐term meteorological effects may overwhelm effects related to nutrient reduction and changes in prey densities may partially offset the benefits of decreased hypoxic conditions.

The relative impacts of nutrient loads and invasive species on a Great Lakes food web: An Ecopath with Ecosim analysis

Excessive nutrient loads and species invasions pose significant threats to productivity and function of Great Lakes aquatic ecosystems. We used an Ecopath and Ecosim model to analyze impacts of changes in phosphorus loads, and dreissenid mussels and alewife biomass on the Saginaw Bay food web, Lake Huron. We configured the food web model in Ecopath with pre-dreissenid (1990) data on organism biomass, production, consumption, and diet from federal and state agency surveys and other sources. We conducted 70-year simulations in Ecosim of single factors (nutrients, alewives, and dreissenids) and their combinations. Phosphorus load scenarios were run with high (1970s), average (current), and low (target) levels; alewife scenarios were run with double the 1990–2003 average biomass, 1990–2003 average biomass, and alewife absence; dreissenid scenarios were run with the 1990–1996 average biomass, current (2009–2010) biomass, and dreissenid absence. Results indicated that phosphorus loads were positively correlated with simulated biomass of most food web groups, and alewife biomass was negatively correlated with biomass of most fish groups and macrozooplankton. Dreissenid impacts were most severe on lower trophic levels but were relatively minor for fish groups compared with nutrient and alewife scenarios. Dreissenids had little effect on fish because Chironomids, which feed on detritus and are the main component of fish diets, were not affected by dreissenids. Our results suggest that, under current conditions of absence of alewives and reduced dreissenid biomass, the target nutrient loads established in 1978 would not sustain current fishery harvests in Saginaw Bay given food web changes caused by invasive species.

A simple 1-dimensional, climate based dissolved oxygen model for the central basin of Lake Erie

A linked 1-dimensional thermal-dissolved oxygen model was developed and applied in the central basin of Lake Erie. The model was used to quantify the relative contribution of meteorological forcings versus the decomposition of hypolimnetic organic carbon on dissolved oxygen. The model computes daily vertical profiles of temperature, mixing, and dissolved oxygen for the period 1987–2005. Model calibration resulted in good agreement with observations of the thermal structure and oxygen concentrations throughout the period of study. The only calibration parameter, water column oxygen demand (WCOD), varied significantly across years. No significant relationships were found between these rates and the thermal properties; however, there was a significant correlation with soluble reactive phosphorus loading. These results indicate that climate variability alone, expressed as changes in thermal structure, does not account for the inter-annual variation in hypoxia. Rather, variation in the production of organic matter is a dominant driver, and this appears to have been responsive to changes in phosphorus loads.

Great Lakes Cladophora in the 21st century: same algae—different ecosystem

Nuisance growth of the attached, green alga Cladophora was considered to have been abated by phosphorus management programs mandated under the Great Lakes Water Quality Agreement. The apparent resurgence of nuisance growth in Lakes Erie, Michigan and Ontario has been linked conceptually to ecosystem alterations engineered by invasive dreissenid mussels ( Dreissena polymorpha and D reissena bugensis). Here, we apply contemporary modeling tools and historical water quality data sets in quantifying the impact of long-term changes in phosphorus loading and dreissenid-mediated changes in water clarity on the distribution and production of Cladophora. It is concluded that reductions in phosphorus loading in the pre-dreissenid period achieved the desired effect, as model simulations were consistent with the biomass declines reported from the early 1970s to the early 1980s. These declines were, however, largely offset by dreissenid-driven changes in water clarity that extended the depth of colonization by Cladophora, increasing total production. We were not able to isolate and quantify the significance of dreissenid mediation of phosphorus cycling using the historical database. Phosphorus management remains the appropriate mechanism for reducing nuisance levels of Cladophora growth. The development of action plans will require an improved understanding of nearshore phosphorus dynamics such as might be obtained through regular monitoring of soluble reactive phosphorus levels, internal phosphorus content and Cladophora biomass in impacted nearshore regions of the Great Lakes.

The M-NIP: a macrophyte-based Nutrient Index for Ponds

In Swiss ponds, eutrophication represents one of the major threats to biodiversity. A biological method to assess the trophic state would, therefore, be particularly useful for monitoring purposes. Macrophytes have already been successfully used to evaluate the trophic state of rivers and lakes. Considering their colonizing abilities and their roles in pond ecosystem structure and function, macrophytes should be included in any assessment methods as required by the European Water Framework Directive. Vegetation survey and water quality data for 114 permanent ponds throughout Switzerland were analysed to define indicator values for 113 species including 47 with well-defined ecological response to total water phosphorus (TP). Using indicator values and species cover, a Macrophyte Nutrient Index for Ponds (M-NIP) was calculated for each site and assessed with both the original pond data set and a limited validation data set. The resulting index performed better when considering only species with narrow responses to TP gradient and was more applicable, but less accurate when including all species. Despite these limitations, the M-NIP is a valuable and easy tool to assess and monitor the nutrient status of Swiss ponds and was shown to be robust and relatively sensitive to slight changes in phosphorus loading with a validation subset.

Response in the water quality of the Salton Sea, California, to changes in phosphorus loading: an empirical modeling approach

Salton Sea, California, like many other lakes, has become eutrophic because of excessive nutrient loading, primarily phosphorus (P). A Total Maximum Daily Load (TMDL) is being prepared for P to reduce the input of P to the Sea. In order to better understand how P-load reductions should affect the average annual water quality of this terminal saline lake, three different eutrophication programs (BATHTUB, WiLMS, and the Seepage Lake Model) were applied. After verifying that specific empirical models within these programs were applicable to this saline lake, each model was calibrated using water-quality and nutrient-loading data for 1999 and then used to simulate the effects of specific P-load reductions. Model simulations indicate that a 50% decrease in external P loading would decrease near-surface total phosphorus concentrations (TP) by 25–50%. Application of other empirical models demonstrated that this decrease in loading should decrease near-surface chlorophyll a concentrations (Chl a) by 17–63% and increase Secchi depths (SD) by 38–97%. The wide range in estimated responses in Chl a and SD were primarily caused by uncertainty in how non-algal turbidity would respond to P-load reductions. If only the models most applicable to the Salton Sea are considered, a 70–90% P-load reduction is required for the Sea to be classified as moderately eutrophic (trophic state index of 55). These models simulate steady-state conditions in the Sea; therefore, it is difficult to ascertain how long it would take for the simulated changes to occur after load reductions.

Response of calcareous Nagawicka Lake, Wisconsin, to changes in phosphorus loading

Nagawicka Lake is a 400-ha, phosphorus (P)-limited, calcareous lake (hardness of 300 mg/L CaCO3) in Wisconsin. Because of concern over potential degradation in water quality associated with urban development in the watershed, a study was conducted to determine the effects of past and future changes in P loading on the lake's water quality through the use of empirical eutrophication models. Six existing empirical P models consistently overestimated total P (TP) concentrations in the lake by a factor of about 2 over a range in external P loading because the models do not account for the unique properties of calcareous lakes: co-precipitation of P with calcite and negligible release of P from the deep sediments. Confirmation of the calcite mechanism was proven by analysis of sediment cores. Once the results were adjusted for the consistent biases, other conventional empirical models fairly accurately predicted the measured chlorophyll a concentrations (CHL) and Secchi depths in the lake. The models, adjusted for the consistent overestimation of TP, were then used to predict the effects of increases and decreases in P loading. Total P and CHL were predicted to decrease or increase by a % similar to the % change in P loading to the lake; however, these relations may become very nonlinear with increases in P loading >100%. Because the natural buffering capacity resists eutrophication caused by P loading, roughly twice the P loading can be permitted in oligotrophic calcareous lakes than in noncalcareous lakes before eutrophication thresholds are exceeded.

Evaluation of recent limnological changes at Lake Apopka

Recent changes in submersed macrophytes and water quality variables have been offered as the strongest evidence that the current restoration program at Lake Apopka will be effective (Lowe et al., 2000); however, the new beds of submersed plants in Lake Apopka are found only on hard substrates on the fringes of the lake within 40 m of shore and are protected from waves by cattails (Typha spp.). They occupy only 0.02% of the lake area, and there is no indication that they can colonize the flocculent sediments that make up 90% of the lake area. There is no correlation between annual inputs of phosphorus and total phosphorus concentrations in the lake, and patterns of change in chlorophyll and other water quality variables do not follow changes in phosphorus loads. Rather than reflecting decreases in phosphorus loading, the recent changes could be related to the harvest of benthivorous fish or are just the normal fluctuations found in lakes that have not been perturbed. Regardless of the reason the macrophytes were lost in the 1940s, the new analyses confirm our previous findings that the high turbidities in Lake Apopka are due to the resuspension of sediments, and that the fluid mud cannot support the colonization of submersed aquatic macrophytes. Even without the fluid mud, the target phosphorus concentration of 55 mg m−3 is too high to bring about the restoration of the former macrophyte beds in the lake.

Strategies to Rehabilitate Lake Simcoe – Modelling Phosphorus Loads, Remedial Measures and Control Options

ABSTRACT Average annual total phosphorus loads to Lake Simcoe are estimated at 100 metric tons. Urban sources of phosphorus such as water pollution control facilities and urban stormwater runoff account for approximately 30% of the total loading. Rural sources such as runoff from agricultural lands, leachate from septic systems, atmospheric deposition and soil erosion contribute the remaining 70%. A target load of 75 metric tons per year has been proposed to ensure an end-of-summer deep water dissolved oxygen concentration of 5.0 mg/L. To achieve the target load, it is necessary to reduce the export of phosphorus from the major controllable sources by 25 metric tons per year. Remedial measures and phosphorus control options to reduce point and non-point sources include controlling agricultural runoff, and erosion and urban stormwater runoff. Several management strategies have been evaluated using a GIS-assisted computer model called HYDROSIM which predicts changes in phosphorus loading in response to implementation of remedial measures within the Lake Simcoe watershed. Management scenarios examined the effectiveness of remedial options based on present and future conditions to ensure that the target load is achievable and sustainable. Modelling results indicate that the most substantial loading reductions can be achieved by controlling urban stormwater runoff and cropland soil erosion. Based on the implementation of an aggressive management program, the target load of 75 metric tons per year is considered to be achievable and can be maintained into the future.

Using carbon isotopes of bulk sedimentary organic matter to reconstruct the history of nutrient loading and eutrophication in Lake Erie

Lacustrine productivity in Lake Erie was reconstructed using measurements of V3C of sedimented organic C (S13C,,,) and non-apatite inorganic P (NAIP) in three cores. Inferred changes in lacustrine productivity were related to historic changes in phosphorus loading. P loading increased slowly after forest clearance and early settlement in the late 18OOs, then increased exponentially from the late 1940s to early 197Os, and finally decreased after the mid- 1970s in response to management practices implemented to improve water quality. Similarly, the sediment accumulation rate of NAIP increased rapidly during the 1940s and 195Os, peaked during the late 1960s and early 197Os, and then decreased after the mid-1970s. The signal of 613C,, normalized to account for the historic 1.4o/oo depletion in V3C of atmospheric CO, mirrors that for accumulation of NAIP in sediments. Our results show that paleoproductivity peaked in the lower Great Lakes during the mid- 1970s but has since declined as a result of P abatement programs. Inferred trends for NAIP and 613C Orgc are those predicted in P-limited lacustrine systems and demonstrate that the carbon isotopic ratio of organic C can be used as a proxy for paleoproductivity in large, deep lakes.

Temporal and Seasonal Trends in Nutrient Dynamics and Biomass Measures in Lakes Michigan and Ontario in Response to Phosphorus Control

Results from long-term ecological monitoring studies on Lake Michigan (1983–92) and Lake Ontario (1981–92) were compared with regard to changes in phosphorus loads. In Lake Ontario, total phosphorus (TP) loads decreased from 14 000 t∙yr−1 in 1970 to 7500 t∙yr−1 in 1981, and correspondingly, midlake TP concentration decreased from 25 to 16 μg∙L−1 From 1981 to 1991 TP loads remained around 7500 t∙yr−1; however, TP concentration continued to decline from 16 to 10 μg∙L−1. Similarly, mean summer particulate organic carbon (POC), chlorophyll a (CHLa), and nitrate utilization rate decreased by approximately 40, 20, and 50%, respectively. Conversely, silica utilization rates increased markedly after 1983. In Lake Michigan, TP loads also decreased by around 50% from 1974 to 1990 (2000 t∙yr−1); however, TP concentrations at our 100-m station in the southern basin increased during the study period from around 4 to 8 μg∙L−1 There were no distinct trends in CHLa or nutrient utilization patterns; however, POC levels decreased sharply after 1987. Overall, silica utilization rates in Lake Michigan were 50% higher than in Lake Ontario (14.7 vs. 9.6 μg∙L−1∙d−1), whereas nitrate utilization rates were only half (1.4 vs. 4.1 μg∙L−1∙d−1).

Recent Changes in Lake Erie (North Shore) Phytoplankton: Cumulative Impacts of Phosphorus Loading Reductions and the Zebra Mussel Introduction

Analyses of phytoplankton samples collected weekly and year-round at municipal water supply intakes in Lake Erie have shown a response to long-term changes in phosphorus loading and the more recent invasion of zebra mussels. Total phytoplankton densities in the western basin of Lake Erie declined from about 5,000 Areal Standard Units (A.S.U.)/mL during the late 1960s to less than 1,000 A.S.U./mL by the mid-1980s and coincided with declines in total phosphorus inputs to the western basin of about 50%. Similar declines were not observed at sites in the central and eastern basins; however, a further dramatic decline (>90%) at all four Lake Erie sites during 1988-1990 coincided with the invasion of the lake by zebra mussels ( Dreissena polymorpha). Similar declines in phytoplankton were not observed at reference sites in southern Lake Huron, where zebra mussels were not abundant. In the western basin, chlorophyll a concentrations of <1 μg/Lfor most of the April to September period of 1991 were typical of oligotrophic areas of the upper Great Lakes. The proportional representation by the dominant classes of algae remained unchanged after the zebra mussel invasion indicating that all classes of algae were equally affected, including the large colony-forming diatoms that dominated the phytoplankton of the western basin in previous years.

Historical Nutrient Enrichment of Lake Ontario: Paleolimnological Evidence

Recent studies of Lake Ontario show four periods of nutrient enrichment that can be identified from the sediment record in this phosphorus-limited system: pristine phosphorus loads (early 1800s before European settlement), moderate increase in phosphorus loading after settlement (beginning approximately 1850), exponential increase in phosphorus loading from urban sources (approximately 1940–70), and decreased phosphorus loading as the result of phosphorus abatement strategies (beginning in mid-1970s). Paleolimnological data are used to infer new paradigms about historical dynamics and cycling of major nutrients. The temporal pattern of organic carbon production closely parallels changes in phosphorus loading. Silica supplies which were replete for diatom production before forest clearance in the mid-1800s became limiting for diatom production in the summer epilimnion after 1865 and in the water column after 1950. Silica reserves were depleted by increased diatom production and sedimentation that resulted from increased phosphorus loading. Biologically induced precipitation of calcite began after 1940 as an indirect effect of increased urban phosphorus loading on primary productivity. Calcite began to be precipitated when historical increases in CO2utilized for primary productivity increased epilimnetic pH and the calcium carbonate saturation product was exceeded.

The impact of internal phosphorus loading on the restoration of Trout lake

AbstractThe accelerated eutrophication of many lakes by society is a problem of increasing concern. The increase in photosynthetic productivity may decrease water clarity, alter dissolved oxygen profiles, and decrease the aesthetic value of a lake. For those lakes which possess high levels of water quality, the need for lake management arises. The first step in developing management techniques for any lake is to collect baseline data—primarily measurements of temperature, dissolved oxygen, transparency, and calculation of a lake's morphometric parameters. Beaulac, Reckhow, and Simpson (1980) [1] indicate that the analysis of lake water nutrient concentration (phosphorus/nitrogen) and calculation of annual nutrient budgets are important additions to baseline data. By studying a lake and its watershed, relationships fundamental to the development of lake prediction models may be determined which operate as a function of nutrient–related parameters such as the areal phosphorus and water loading to a lake.Quantitative changes in phosphorus loading can be interpreted to provide changes in lake water phosphorus concentration and subsequently trophic status. Predictions made through the use of such models serve as a basis for management decisions.

A Nine-Year Study of the Phytoplankton of the Eutrophic and Non-Stratifying Loch Leven (Kinross, Scotland)

(1) Observations from 1968 to 1976 at mainly weekly intervals on the phytoplankton of the shallow, eutrophic and non-stratifying Loch Leven have revealed marked seasonal and annual differences in species-composition and population densities. However, long term trends were apparent, with decreasing concentrations of chlorophyll a, total dry weight and total volume of phytoplankton, although an increase in the latter two features in 1976 coincided with a massive growth of a pale form of Oscillatoria agardhii Gomont. (2) Trends were apparent also in increasing size of dominant algae and decreasing total numbers of individuals producing the various population maxima. A 3000-fold increase in size has accompanied the change towards large species, e.g. Melosira ambigua (Grun.) Muller, Anabaena flos-aquae Brέb. (ex Born. et Flah.), and Oscillatoria agardhii, which have progressively replaced `nano' forms, e.g. Synechococcus nov. sp., Oscillatoria redekei van Goor and some unicellular centric diatoms. Recent population maxima have rarely exceeded 104 individuals per ml, in sharp contrast to earlier growths commonly of 105-106 individuals per ml. (3) Considerable variation in the percentage chlorophyll a of crop dry weight (0.32-1.96), and the ratios of chlorophyll a to volume ( 12 \mu g mm^{-3}) and of dry weight to volume (0.31-1.32 mg mm-3), was associated with the continual changes in species-composition. (4) General features of the algal plankton are discussed in relation to the gross physical and chemical characteristics of the loch, whilst some of the observed trends in plankton quantity and quality are considered in relation to changes in phosphorus loading (a reduction of approximately 1.0 g m-2 P per annum since 1972) and in zooplankton quality (a shift from a Cyclops- to a Daphnia-dominated community since 1971). (5) The need for long-term studies based on close time-interval sampling for information on species and populations is emphasized; one source of misinterpretation of results if species-variation is not taken into account is discussed and illustrated with the use of a simple theoretical model.

A Test of a Simple Nutrient Budget Model Predicting the Phosphorus Concentration in Lake Water

The total phosphorus budgets for a number of lakes in the Haliburton–Kawartha region of southern Ontario were measured over a 20-mo period. These data, combined with the lakes' morphometry and water budgets, were used to test a simple nutrient budget model similar to that proposed by Vollenweider (1969) purporting to predict the total phosphorus concentration in lakes. Except in the case of two very shallow lakes [Formula: see text], the concentrations predicted by the model were very close to those measured in the lakes at spring overturn. Additional data from the literature supported the belief that this model could be used effectively for oligotrophic and mesotrophic lakes. Its value lies in the fact that quantitative changes in phosphorus loading can be interpreted in terms of changes in phosphorus concentration, which in turn, can be related to changes in parameters that reflect the lake's trophic state such as summer chlorophyll a concentration.