High nitrogen to phosphorus ratio in a Texas coastal river: origins and implications for nutrient pollution sources and exports

Inorganic forms of nitrogen and phosphorus, oxygen levels, suspended solids, and planktonic primary productivity were monitored in Guadalupe River, a major waterway in southeast Texas. Our measurements have shown elevated levels of inorganic nutrients, with soluble reactive phosphorus reaching into 30 μg/L. Curiously, those elevated levels of nutrients combined with unexpectedly high nitrogen to phosphorus (N:P) ratio and low planktonic primary productivity. We attribute those phenomena to suspended solids acting as a selective sink for phosphorus while preventing effective photosynthesis in planktonic algae. At the same time, the potential for nitrogen removal is limited by abundant oxygen present in the water. This combination of low light, selective phosphorus removal, and high oxygen levels suggest that the Guadalupe River is likely to effectively export nitrogen, but not phosphorus into the estuary.