Temporal and Spatial Variations in Phosphorous Concentration within the Red Cedar River Watershed

Abstract

Phosphorus is one of the key nutrients in sustaining healthy plant growth; however, if too much phosphorus is present within the a water system, it can lead to massive algal blooms. Excessive algae growth can release toxins and deplete dissolved oxygen concentrations as the algae decays. This leads to poor water quality, as seen in the lower Red Cedar River Watershed.

Previous research in the Red Cedar watershed has not investigated the background contribution of phosphorus from groundwater sources compared to surface water. Our research explores and identifies groundwater and surface water interactions.

Land use practices affect when phosphorus is transported downstream. In the Wilson Creek watershed the highest concentrations of soluble reactive phosphorus (SRP) and total phosphorus (TP) were observed downstream of sites where cattle were pastured, with the highest TP concentrations on the hottest days.

In the South Fork Hay River and Tiffany Creek watersheds the highest concentrations of SRP and TP were associated with large precipitation events. Rainfall events can cause sheet, rill, and gully erosion, which are able to transport phosphorus that is attached to sediment particles. Rain events also lead to increased discharge in streams, which can move phosphorus attached to sediment in the streambed, stream banks, and in larger events, even the floodplain.

We found elevated SRP and TP concentrations in some groundwater samples. A potential groundwater phosphorus source is located near the contact between the Mt. Simon and Eau Claire formations, which contain abundant phosphatic brachiopod shells. The widespread distribution of these bedrock units suggests background TP and SRP testing and sourcing should be done in order to best estimate total maximum daily phosphorus loads from individual streams.