Abstract
Remediation and restoration of the Upper Clark Fork River (UCFR) is occurring under nutrient-rich conditions associated with non-point source and sewage treatment inputs. Restoration is designed to enhance river-floodplain interaction with potential influences on river nutrient loads. Assessment of the long-term record for nitrogen (N) and phosphorus (P) illustrate that the upper river consistently exceeds water quality standards for total N (300 μg N/L) and total P (20 μg/L P). However, data from the past three decades also show substantial reduction in nitrate-N loads during summer and autumn despite inputs from tributaries and sewage treatment facilities. During these time periods, benthic algal standing crops can be substantial (150 – 275 mg/m2 as chlorophyll) and measures of primary production support the potential for algal uptake to remove inorganic N and generate high atomic N:P ratios. Nutrient-diffusing assays suggest N-limitation of algal growth despite an overabundance of total N in the river water. Along with a plentiful supply of P, these conditions are optimal for the growth and proliferation of N-fixing microbes (i.e., bluegreen algae). Genetic assessment of epilithic biofilms along a 10-km reach near Drummond shows that bluegreens are indeed an abundant and diverse part of the microbial community. Preliminary assessment of the potential for N-fixation to add to nutrient enrichment and promote nuisance algal blooms points to the need to investigate elemental interactions and manage multiple water quality issues simultaneously as restoration continues concomitant with development of waste water and sewage treatment capacity on the UCFR.
Start Date
24-4-2015 11:30 AM
End Date
24-4-2015 12:00 PM
Document Type
Presentation
Nutrient dynamics in the Upper Clark Fork River
Remediation and restoration of the Upper Clark Fork River (UCFR) is occurring under nutrient-rich conditions associated with non-point source and sewage treatment inputs. Restoration is designed to enhance river-floodplain interaction with potential influences on river nutrient loads. Assessment of the long-term record for nitrogen (N) and phosphorus (P) illustrate that the upper river consistently exceeds water quality standards for total N (300 μg N/L) and total P (20 μg/L P). However, data from the past three decades also show substantial reduction in nitrate-N loads during summer and autumn despite inputs from tributaries and sewage treatment facilities. During these time periods, benthic algal standing crops can be substantial (150 – 275 mg/m2 as chlorophyll) and measures of primary production support the potential for algal uptake to remove inorganic N and generate high atomic N:P ratios. Nutrient-diffusing assays suggest N-limitation of algal growth despite an overabundance of total N in the river water. Along with a plentiful supply of P, these conditions are optimal for the growth and proliferation of N-fixing microbes (i.e., bluegreen algae). Genetic assessment of epilithic biofilms along a 10-km reach near Drummond shows that bluegreens are indeed an abundant and diverse part of the microbial community. Preliminary assessment of the potential for N-fixation to add to nutrient enrichment and promote nuisance algal blooms points to the need to investigate elemental interactions and manage multiple water quality issues simultaneously as restoration continues concomitant with development of waste water and sewage treatment capacity on the UCFR.