Predicting Nitrogen and Phosphorus Concentrations using Chlorophyll-a Fluorescence and Turbidity

Author(s): Andrews, C.; Kröger, R.; Miranda, L.

Agricultural practices and land modification introduce excess nutrient and sediment loads into inland watersheds. Modification of tributary streams and rivers within these watersheds decreases the ability of floodplains to respond to increased loads. Therefore, large amounts of nutrients and sediments are transferred to coastal aquatic systems. Aquatic systems are facing increased nuisance algal growth and premature senescence leading to hypoxic conditions, threatening recreational and commercial fish yields. Furthermore, sedimentation and turbidity create intolerant conditions for aquatic organisms, and can trap phosphorus in these systems. To address these issues, states are developing nutrient criteria for inland waters. As inland water bodies are numerous, the usefulness of such criteria is dependent on efficient monitoring. We investigated the potential use of a handheld chlorophyll-a (chl-a) fluorometer as an estimator of total phosphorus (TP) and total nitrogen (TN) in oxbow lakes of the Mississippi Alluvial Valley. Several adjustments were explored to improve the ability of the fluorometer to accurately represent chl-a. Past studies in Mississippi lakes have shown a poor relationship between TP and chl-a (r2 = 0.18), but a moderate relationship between TN and chl-a (r2 = 0.53). The poor TP-chl-a relationship is partially attributable to naturally high levels of phosphorus and turbidity in the region. We found the relationships between chl-a and nutrient concentrations were improved in oxbow lakes; adding covariates such as turbidity and suspended solids further improved predictability. Estimating TP and TN with in-situ handheld-meter measurements of chl-a supplemented with measures of suspended solids may, in many cases, be adequate for temporal or spatial monitoring of nutrients in oxbow lakes.
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1 Best Management Practices #1
2 Delta Water Assessment
3 Flood Assessment & Mgmt.
4 Wetlands
5 Watershed Mgmt. #1
6 Non-Point Source Assessment
7 Modeling
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9 Best Mgt. Practices #2
10 Delta Water Conservation
11 Sedimentation
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13 Watershed Mgt. #2
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