Spatial and Temporal Variations in Phosphorus Loads in the Illinois River Basin, Illinois USA

Abstract

Total phosphorus (TP) loads in many rivers in the north‐central United States have increased, including the Illinois River at Valley City, Illinois, USA, which increased 39% from the periods 1989–1996 to 2015–2019 despite efforts to reduce loads from point and nonpoint sources. Here, we quantify long‐term variations in phosphorus (P) loads in the Illinois River and its tributaries and identify factors that may be causing the variations. We calculated river loads of dissolved (DP) and particulate P (PP), total and volatile suspended solids (TSS and VSS), and other potentially related constituents at 41 locations. DP loads generally increased and PP and TSS loads generally decreased from 1989–1996 to 2015–2019. During 1989–1996, P accumulated in the lower basin between Marseilles and Valley City (excluding monitored tributaries). This portion of the basin is very flat and accumulates sediment. During 2015–2019, this section shifted from being a net sink to being a net source of P, accounting for 78% of the increased TP load at Valley City. We present evidence supporting several mechanisms that could have caused this shift: increased DP and chloride loads, reduced sulfate and nitrate concentrations influencing ionic strength and redox potential in the sediments, and increased VSS loads at Valley City possibly indicating greater algal production and contributing to hypoxia in lower river sediments. Additional research is needed to quantify the relative importance of these mechanisms.

River Control Points for Algal Productivity Revealed by Transport Analysis

“…The Kankakee and Fox Rivers had more influence, and additional information helped refine C IN estimation. The Kankakee River can contribute more than 50% of the flow in Reach 1, but primary productivity is relatively low compared to the Illinois River (Choi et al., 2022), likely because turbidity is relatively high and phosphorus is relatively low (McIsaac et al., 2023). We selected C IN = 0 μg chl‐ a L −1 as the best estimate for the Kankakee River.…”

Metabolism Regimes in Regulated Rivers of the Illinois River Basin, USA

“…River metabolism is relevant to assessing causes and consequences of eutrophication such as hypoxia, serving as an early warning indicator of changing river functions and health as well as indicating shifts in greenhouse gas emissions 1,2 . Here we focused on metabolism of regulated rivers in the Illinois River basin (IRB) where river algal blooms and associated toxins have been reported [3][4][5][6][7] . To quantify metabolism, the rate of oxygen production and consumption in the aquatic system is measured over time to estimate gross primary productivity (GPP) and ecosystem respiration (ER).…”

“…The Illinois River is substantially regulated by a series of locks and dams to maintain minimum water levels for navigation through the upper Illinois River as it enters the Des Plaines River tributary and headwaters of the Chicago Area Waterway System (CAWS). Not surprisingly, water quality and ecological conditions are substantially impaired in IRB rivers, including high nutrients and suspended sediments 3,4 . Large tributaries of the Illinois River include the Kankakee River which U.S. Geological Survey, earth System Processes Division, Reston, VA, USA.…”

Integrated Agricultural Practices and Engineering Technologies Enhance Synergies of Food-Energy-Water Systems in Corn Belt Watersheds

“…The food, energy, and water systems (FEWS) in Corn Belt watersheds are multifunctional systems that jointly produce crops (mainly corn and soybean), food products, animal feed, ethanol, water (for both the environment and domestic use), and other ecosystem services. , These functions generate socioeconomic benefits along with high energy consumption, nutrient discharge, , and interconnected risks to food, energy, and water sectors. , Specifically, crop production in the region faces challenges from weather variability, pests, input price fluctuations, nutrient loss, soil erosion, and calls to reduce fertilizer usage. , Intensive fertilizer use in crop production and expansion of corn-based ethanol production have led to high nutrient loading to water bodies and require increased energy use and costs for drinking water and wastewater treatment while accelerating aquatic vegetative growth and ecosystem disruptions . Phosphorus (P), a key component of fertilizers and a major contributor to the harmful algal blooms in the Great Lakes and the “Dead Zone” in the Gulf of Mexico, plays a complicated role within the FEWS. , A particular concern for the region is the so-called P paradoxtoo much P from agricultural production and food processing polluting water bodies despite a decline of phosphate rock reserves for P fertilizer. , For example, the Sanitary District of Decatur, which treats wastewater from ADM and other major food companies, is one of the largest point sources of P in Illinois, and it contributes to the increased P load to the Illinois River . Other substances (e.g., N and sediment) that affect water quality should be included in analyses and discussions evaluating strategies for water quality improvement.…”

“…14,15 For example, the Sanitary District of Decatur, which treats wastewater from ADM and other major food companies, is one of the largest point sources of P in Illinois, and it contributes to the increased P load to the Illinois River. 16 Other substances (e.g., N and sediment) that affect water quality should be included in analyses and discussions evaluating strategies for water quality improvement. However, the opportunities for recovering P from point sources, which could reduce both riverine P loads and P demand from declining geologic reserves, have not been wellstudied and deserve in-depth analysis to address potentially competing challenges of food production and environmental quality.…”