The City of Gresham, Oregon has implemented constructed wetlands around the area as an attempt to collect, filter, and purify water from different sources such as rain, agricultural waste, and domestic waste. We focused our research on three different facilities: Columbia Slough Water Quality Facility (CSWQF), Fairview Creek Water Quality Facility, and Brookside Water Quality Facility. For each of these, we conducted tests and looked at the concentration levels for nitrogen and phosphorus nutrients such as NH3-N (ammonium), NO3-N (nitrate), TKN (total Kjeldahl nitrogen), O-PO4 (phosphate), and Total P (total phosphorus), as well as heavy metals like Total Cu (total copper) and Total Zn (total zinc).
It was essential to consider different factors that could influence the water quality at these facilities, for example, low vegetation area, forested area, and developed area percentages, as well as antecedent rainfall for the 24, 48, 72, 96, and 120 hour periods. Rain was a huge factor because runoffs caused by rainy days carry a lot of debris and harmful nutrients and metals into streams, it is fundamental to understand the relation between rainfall and chemical concentrations in the wetlands because they tend to be higher at the beginning of rain periods because of the first-flush where there is buildup debris, sedimentation, nutrients, and metals. The constant flow of water dilutes concentration levels.
Wetlands become a habitat for different species, such as beavers. Beaver activity was another important factor when looking at the CSWQF, beaver dams in the Columbia Slough facility help to catch heavy metals from flowing into the streams. Beavers were found to improve the quality of water due to this, a Mann-Whitney U test was conducted to find the significance between beavers and concentration levels.
After gathering all of the necessary information and considering all these factors for each of the facilities, we conducted a Spearman's Rank correlation analysis to learn what factors have a bigger impact on which concentrations. Some of our findings were that the 24-hour rainfall was significant for NO3-N concentration difference and forested area significant relation with O-PO4 concentration difference.
Wetlands are doing a great job at filtering water and their implementation should be wider around the state and even the country. As a community, it is also important to be mindful of the water waste we produce, the fertilizer use in our lands, and any other form of littering in urban areas.
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Barajas, Evelyn and Gonzalez, Michael, "Water Quality Land Cover Change and Water Quality in Wetlands at the City of Gresham, Or" (2023). altREU Projects. 15.