HOW...Nutrient pollution in Hicklin Lake

 Nutrient buildup (most importantly Phosphorous) in Hicklin Lake is the driving cause behind the ecological problems seen in today. 

I. IDENTIFIED SOURCES OF EXCESS NUTRIENTS

External sources (From outside the lake): Organic matter, soil erosion, pet/waterfowl waste, atmospheric deposition, lawn fertilizers (Sims)

Internal sources (From inside the lake): Decaying aquatic plants, sediment release (caused by phytoplankton taking up Phosphorous from the sediment and traveling up through the water column) (Sims)

II. MEASURED NUTRIENT LEVELS:

Numerical proof that the health of Hicklin Lake isn't where we want it to be

PHOSPHOROUS VALUES

Phosphorous is generally the limiting nutrient in algal growth and proliferation meaning that in the presence of excess Phosphorous, cyanobacteria growth exceeds normal levels and often forms blooms, the danger of which will be discussed later. 

The figure below provides levels of Phosphorous in Hicklin Lake measured throughout the years of 1996, 1997, 1998 and 2004. Seasonal variation in Phosphorous levels are shown. The red line represents King County's management goal for average Phosphorous levels (Sims). Actual phosphorous levels clearly overshoot this goal at all times of the year. (Sims)

TSI VALUES

Another measurement commonly used to compare lake health is TSI, an index combining 3 important measurable factors: phosphorous concentration, chlorophyll a concentration, and Secchi depth transparency data. The TSI index that results allows for the following classifications: Oligotrophic- Low biological activity (TSI< 40), Mesotrophic- Medium biological activity (TSI 40-50), Eutrophic- High biological activity (TSI >50) (Sims)

This figure compares 2004 TSI values with the King County average goal of 50 (Sims). The data necessary for these measurements have only recently been gathered meaning that pre-development TSI values are not know. (Sims)

DISSOLVED OXYGEN (DO) LEVELS

High Phosphorous levels (TP) correspond to low levels of dissolved Oxygen (DO) in Hicklin Lake. This phenomenon is caused by algal blooms which have an extremely short life cycle. When they die, decomposer populations proliferate and use up the water's oxygen in the process (Leng). Low DO means lake water cannot support healthy fish or other aquatic organism populations. 

This table reveals that Phosphorous levels are particularly high in late summer/early fall months and at greater depths. Low DO levels accompany high TP. (Sims)