laboratory-determined-phosphorus-flux-from-lake-sediments-as-measure

Laboratory-determined Phosphorus Flux from Lake Sediments as a Measure of Internal Phosphorus Loading

Eutrophication is a water quality issue in lakes worldwide, and there is a critical need to identify and control nutrient sources. Internal phosphorus (P) ...

Grand Valley State University

Periphyton communities have received relatively little attention in lake ecosystems. However, evidence is increasing that they play a key role in primary productivity, nutrient cycling, and food web interactions. This review summarizes those findings and places them in a conceptual framework to evaluate the functional importance of periphyton in lakes. The role of periphyton is conceptualized based on a spatial hierarchy. At the coarsest scale, landscape properties such as lake morphometry, influence the amount of available habitat for periphyton growth. Watershed-related properties, such as loading of dissolved organic matter, nutrients, and sediments influence light availability and hence periphyton productivity. At the finer scale of within the lake, both habitat availability and habitat type affect periphyton growth and abundance. In addition, periphyton and phytoplankton compete for available resources at the within-lake scale. Our review indicates that periphyton plays an important functional role in lake nutrient cycles and food webs, especially under such conditions as relatively shallow depths, nutrient-poor conditions, or high water-column transparency. We recommend more studies assessing periphyton function across a spectrum of lake morphometry and trophic conditions.

Periphyton function in lake ecosystems.

Groundwater withdrawal has major economic, social, and environmental implications. In Michigan, recent legislative activity has begun to address the issue of groundwater sustainability. However, more hydrologic data are needed to help inform policy and legislation. A study was conducted in Mecosta County, Michigan to: (1) determine if a relationship could be established between land use/land cover and groundwater quality; and (2) develop a conceptual model for the shallow groundwater system of the study region. In general, groundwater quality was good, with below detection levels of E. coli, low total bacterial counts, and relatively low nutrient concentrations. No statistically significant associations were found between the bacterial numbers and either land use or the physical/chemical attributes measured, which may be because the scale of our spatial analysis was too coarse to detect patterns. Finer-scale, localized processes may have a greater influence on microorganism growth and abundance than coarser-scale, regional processes in this area. Our groundwater analysis suggested that shallow groundwater flow paths are generally consistent with regional surface water flow networks, and that shallow groundwater levels in most of the region have fluctuated within 1-2 m over the past 30 years, with no obvious increasing or decreasing trend.

Environmental analysis of groundwater in Mecosta County, Michigan.

A whole-lake alum treatment was applied to eutrophic Spring Lake during October and November 2005. Eight months later, an ecological assessment of the lake was performed and compared with data collected in 2003 and 2004. Field measurements showed reduced soluble reactive phosphorus (SRP) and total phosphorus (TP) concentrations in the water column the summer after the alum application, but chlorophyll levels and irradiance profiles were not significantly affected. Total macroinvertebrate density declined significantly in 2006 compared with 2004, with chaoborids and oligochaetes experiencing the greatest reductions. Internal phosphorus release rates, measured using sediment cores incubated in the laboratory, ranged from -0.052 to 0.877 mg TP m(-2) d(-1) under anaerobic conditions. These internal loading rates were significantly lower than those measured in 2003 at three out of four sites. Mean porewater SRP concentrations were lower in 2006 than in 2003, but this difference was statistically significant only under aerobic conditions. The NaOH-extractable SRP fraction in the sediment was also significantly lower in 2006 compared with 2003, whereas the HCl-extractable SRP sediment fraction showed the opposite pattern. Overall, these results indicate that the alum treatment effectively reduced internal P loading in Spring Lake. However, water column phosphorus concentrations remain high in this system, presumably due to high external loading levels, and may account for the high chlorophyll levels. An integrated watershed management approach that includes reducing internal and external inputs of P is necessary to address the cultural eutrophication of Spring Lake.

Ecological effects after an alum treatment in Spring Lake, Michigan.

A limnological survey was conducted of Little Black Lake, MI, and its tributaries during summer 2007. This small, shallow lake is located in a rapidly developing area of west Michigan. As such, our analytical approach and recommendations can serve as a model for other similar systems threatened by urbanization. Soluble reactive phosphorus and nitrate concentrations in both the inflows to (during baseflow) and Little Black Lake itself were low (≤0.007 and ≤270 mg/L, respectively). Nutrient concentrations increased during stormflow conditions, although the magnitude of the increase depended on the nutrient and sampling location. Macrophyte growth was extensive throughout most parts of the lake, with Chara and Potamogeton spp. present in most sites; based on the coefficient of conservatism, plant composition was indicative of good water quality conditions. Chlorophyll a concentration averaged 1.7 μg/L in Little Black Lake, with cryptophytes and cyanobacteria being the most dominant members (by biovolume) of the phytoplankton community. The fish community in Little Black Lake was dominated by bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus), with no invasive species observed. Overall, abiotic and biotic conditions indicate that Little Black Lake is in good ecological health despite increasing pressures of urbanization in its watershed. To maintain this status, it is recommended that the local municipalities develop a comprehensive watershed management plan and implement best management practices to limit nonpoint source pollutant loading to Little Black Lake.

An environmental assessment of a small shallow lake (Little Black Lake, MI) threatened by urbanization.

Alum treatment is a lake restoration technique that is used to address internal phosphorus (P) loading. We evaluated the macroinvertebrate density and P release rates from sediment cores in Spring Lake, Michigan, 5 yr after an alum treatment and compared the findings with conditions before and 1 yr after application. Total macroinvertebrate density recovered to the near pre-alum level after the decline that was measured in 2006. Community structure also shifted, with the dominant group changing from oligochaetes before alum treatment to chaoborids in 2010. Chironomid density in 2010 was similar to pre-alum density, but this represented a decline from an elevated density measured in 2006. Ceratopogonid density increased in 2010 compared with the prior samplings, but absolute densities were very low compared with other macroinvertebrate groups. Maximum P release rates from sediment cores in 2010 averaged from 1.68 to 2.81 mg P m d under anoxic conditions. These rates are an order of magnitude lower than before alum was applied, indicating the alum application was still effectively reducing P release rates from sediments in Spring Lake. However, the release rates have increased since 2006, suggesting that alum efficacy may be declining. The NaOH-extractable soluble reactive P fraction has increased since 2006, suggesting that the aluminum hydroxide floc is successfully binding P in the sediments. Despite the low release rates of P from the sediment, water column P and chlorophyll concentrations remain elevated in Spring Lake. This points to the continued need for reductions in external P loads to Spring Lake.

Macroinvertebrate response and internal phosphorus loading in a Michigan Lake after alum treatment.

With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through large-scale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in near-shore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments.

Joint analysis of stressors and ecosystem services to enhance restoration effectiveness.

We considered how Lake Okeechobee, a large shallow lake in Florida, USA, might respond to altered hydrology associated with climate change scenarios in 2060. Water budgets and stage hydrographs were provided from the South Florida Water Management Model, a regional hydrologic model used to develop plans for Everglades restoration. Future scenarios include a 10 % increase or decrease in rainfall (RF) and a calculated increase in evapotranspiration (ET), which is based on a 1.5 °C rise in temperature. Increasing RF and ET had counter-balancing effects on the water budget and when changing concurrently did not affect hydrology. In contrast, when RF decreased while ET increased, this resulted in a large change in hydrology. The surface elevation of the lake dropped by more than 2 m under this scenario compared to a future base condition, and extreme low elevation persisted for multiple years. In this declining RF/increasing ET scenario, the littoral and near-shore zones, areas that support emergent and submerged plants, were dry 55 % of the time compared to less than 4 % of the time in the future base run. There also were times when elevation increased as much as 3 m after intense RF events. Overall, these changes in hydrologic conditions would dramatically alter ecosystem services. Uncertainty about responses is highest at the pelagic-littoral interface, in regard to whether an extremely shallow lake could support submerged vascular plants, which are critical to the recreational fishery and for migratory birds. Along with improved regional climate modeling, research in that interface zone is needed to guide the adaptive process of Everglades restoration.

Alan D. Steinman

Annis Water Resources Institute

Grand Valley State University

Laboratory-determined Phosphorus Flux from Lake Sediments as a Measure of Internal Phosphorus Loading

Alan D. Steinman

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Grand Valley State University

Laboratory-determined Phosphorus Flux from Lake Sediments as a Measure of Internal Phosphorus Loading

Annis Water Resources Institute