Ecosystem Modeling Applied to Nutrient Criteria Development in Rivers

Abstract

Threshold concentrations for biological impairment by nutrients are difficult to quantify in lotic systems, yet States and Tribes in the United States are charged with developing water quality criteria to protect these ecosystems from excessive enrichment. The analysis described in this article explores the use of the ecosystem model AQUATOX to investigate impairment thresholds keyed to biological indexes that can be simulated. The indexes selected for this exercise include percentage cyanobacterial biomass of sestonic algae, and benthic chlorophyll a. The calibrated model was used to analyze responses of these indexes to concurrent reductions in phosphorus, nitrogen, and suspended sediment in an enriched upper Midwestern river. Results suggest that the indexes would respond strongly to changes in phosphorus and suspended sediment, and less strongly to changes in nitrogen concentration. Using simulated concurrent reductions in all three water quality constituents, a total phosphorus concentration of 0.1 mg/l was identified as a threshold concentration, and therefore a hypothetical water quality criterion, for prevention of both excessive periphyton growth and sestonic cyanobacterial blooms. This kind of analysis is suggested as a way to evaluate multiple contrasting impacts of hypothetical nutrient and sediment reductions and to define nutrient criteria or target concentrations that balance multiple management objectives concurrently.

Development of Environmental Thresholds for Nitrogen and Phosphorus in Streams

“…The higher TP threshold for the relative abundance of Diptera + noninsects (0.063 mg L −1 ) is likely due to the fact that this index selects for taxa that are more tolerant of degraded conditions (i.e., increased siltation and eutrophication, and low concentrations of dissolved oxygen) and thus this indicator may be more indicative of transition from mesotrophic to eutrophic conditions. Studies are now beginning to converge around a TP threshold of about 0.02 to 0.06 mg L −1 , above which benthic chl a values increase sharply (e.g., Dodds and Welch, 2000; Dodds et al, 2002, 2006; Hill et al, 2009; Miltner, 2010), although values as low as 0.01 and as high as 0.l mg L −1 TP have been put forward as limits (Stevenson et al, 2008; Carleton et al, 2009). Concentrations of 0.04 to 0.15 mg L −1 TP have also been identified as nutrient thresholds for several benthic invertebrate indicators for Wisconsin wadeable and nonwadeable rivers (Wang et al, 2007; Weigel and Robertson, 2007).…”

Linking Water Quality and Quantity in Environmental Flow Assessment in Deteriorated Ecosystems: A Food Web View

“…This model utilizes differential equations to represent the change of state variables and uses five different libraries to save animal, plant, chemical, site and mineralization parameters respectively. The model also provides Latin hypercube uncertainty analysis, nominal range sensitivity analysis, and time-varying process rates and limitations to photosynthesis for detailed analyses [33], [36]. Hence, Aquatox model has the potential to establish links among water quantity, water quality, and biological response.…”

Environmental flow management strategies based on the integration of water quantity and quality, a case study of the Baiyangdian Wetland, China

“…The growth of each population is determined by environmental conditions, population biomass, and the specific physiological parameters of each population. Relevant physiological parameters used were either taken from the original AQUATOX model or acquired from the biological and ecological literature (Carleton et al, 2009;USEPA, 2014). Most of the state and driving variables include in the integrated model are list in Table 3.…”