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Nutrient Reduction in Wetlands
More than 2 years of monthly water quality testing of the Constructed Wastewater Wetlands at the Oregon Garden have shown a marked decrease in excess nitrate and phosphorous concentrations from Pond A to Pond Y. When the water re-enters the watershed, the nutrient concentrations are usually non-detectable.
Relevant Documents:
Comments
water quality montoring N and P
You might want to consider how to link the nutrient concentrations with a map showing where the various water sampling locations are at your site. I assume that the data graphs show a "downhill" flow, but the accompanying text describes a groundwater contribution at some point in the flow path (not sure where). A map (aerial) could show sampling points, and where the ground water enters the system. Maybe you could also show an "average" value for N and P concentration at each sampling point during the year. In showing typical nutrient concentrations, you might want to divide year into "winter" and "summer", if there is consistent seasonal variation in water flow and/or nutrient concentration.
Question:
Why is water not analyzed for ammonia or ammonium-N (NH3-N or NH4-N; same analysis, sometimes called different names)? In surface water, NH4-N is the basis for summer permits for discharge from wastewater treatment facilities to rivers, because NH4-N is more toxic form of N to fish (more toxic than nitrate-N).
Aerial map and form of Nitrogen
Dan,
Sorry this took so long- still working out kinks in the website settings . . .
Great idea on the map of sampling locations. We'll have to craft something in Publisher. We'll also put together some more recent data, and one with annual averages. Our staff time is limited right now, but we'll get it up as soon as we can. In the meantime, yes, most of the sampling sites are arranged on the graph in downhill order. However, the Oak Grotto serves as a groundwater reference site, not in line with the others and not receiving wastewater. Brush Creek Up stream of the Garden's influence also serves as a pseudo-native reference site. However, Brush Creek is complicated by the Pettit Reservoir, which intersects it shortly above where the Garden connects to Brush Creek.
To answer your question, you are exactly right that discharge permits are based on ammonia, which is WHY we don't test for it. We know already that the water entering our site from the WWTP in Silverton already meets the DEQ established ammonia limits. Therefore, the form of nitrogen that becomes important to know about in our system is nitrate. Both ammonia and nitrate are plant-available forms, but nitrate hangs around longer and can have equally deleterious effects on fish/amphibians/water quality. Ideally we'd probably test for both nitrate and total N, but budget will not allow. Please note, however, that if you look at the absolute values of nitrate in our system, they are usually pretty low even entering our system. I.e. even without the marked reduction in nitrate that the wetlands show, our levels would not be a danger to wildlife, as evidenced by the thriving populations of amphibians and fish in our upper ponds.
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