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

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.

Mary E. Ogdahl

Annis Water Resources Institute

Grand Valley State University

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

Mary E. Ogdahl

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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