Flow‐Dependent Color Patches in a Great Plains River

• Published in: Journal of geophysical research. Biogeosciences 2024-07, Vol.129 (7), p.n/a
• Main Authors: Bruns, Nicholas E., Gardner, John R., Doyle, Martin
• Format: Article
• Language: English
• Subjects: Accumulation; Algae; Aquatic ecosystems; Aquatic habitats; Benthos; Bioaccumulation; Biological activity; Color; Color imagery; Columnar structure; Dam stability; Dams; Dimensional analysis; Dissolved organic matter; Downstream; Ecosystem management; Ecosystem structure; Ecosystems; Heterogeneity; High flow; high frequency sensors; Image processing; large rivers; Phytoplankton; Plankton; river color; River ecology; Rivers; Satellite imagery; Satellite observation; Sediment; Sediments; spatial patterning; Spatial variations; Stream discharge; Stream flow; Suspended sediments; Water circulation; Water color; Water colour; Water column
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2023JG007867

Ecosystem structure and its heterogeneity shape ecosystem processes. Ecosystem heterogeneity has been characterized in smaller stream ecosystems dominated by benthic processes. However, in larger river ecosystems structured by water column characteristics including suspended sediment and phytoplankton, ecosystem heterogeneity has not been directly observed. We assessed flow‐dependent ecosystem structure along 230 km of a large, highly managed Great Plains river (The Kansas River) by analyzing 1‐dimensional, downstream color profiles across flow conditions derived from satellite imagery. River color is a robust metric that reflects the combined state of several important large‐river habitat features, specifically suspended sediment, chromophoric dissolved organic matter, and phytoplankton. We found that at flows above a flow threshold that we call Qpatch (240 m3 s−1), the entire river was uniformly yellow. At flows below Qpatch, the river was generally greener and often had patches of very green water that occurred upstream of run‐of‐river dams. Comparing color with in situ data showed the color patches were likely areas of elevated chlorophyll‐a concentrations from phytoplankton accumulation, indicating that the patches reflected biological processes. Flows were below Qpatch on 77% of days during the period of record (1985–present), indicating that the ecosystem spends significant time in a patchy state. Our findings uniquely demonstrate that the water column characteristics structuring temperate, large‐river ecosystems can be patchy. Plain Language Summary An ecosystem represents a collection of smaller areas, or patches, that play different ecological roles. We can see and walk through patches in forests, however within flowing aquatic ecosystems like large rivers, it is difficult to see and characterize patches. Here, we present direct observations of downstream patches along a river and how they change across streamflow conditions. We measure spatial variation using satellite‐derived water color observations as a proxy for ecosystem properties along a highly managed Great Plains river, The Kansas River. Increases in algae floating in the river should make the river greener, while increases in sediment should make the river more yellow. We found that at high flows above a distinct threshold, the entire river was uniformly yellow. At flows below the threshold, the river was greener and often had particularly green patches behind small, in‐river dams. Com