P. A. Chambers(1), C. Vis(1), R. B. Brua(2), M. Guy(1), J. M. Culp(3), and G. Benoy(4) Environment Canada (1) 867 Lakeshore Blvd., PO Box 5050, Burlington, Ontario L7R 4A6, Canada, (2) 11 Innovation Blvd., Saskatoon, Saskatchewan S7N 3H5, Canada, (3) University of New Brunswick, Department of Biology, P.O. Box #45111, Loring Bailey Hall, Fredericton, New Brunswick E3B 5A3, Canada, (4) Agriculture & Agri-Food Canada, Potato Research Centre, 850 Lincoln Road, PO Box 20280, Fredericton, New Brunswick E3B 4Z7, Canada
Patricia.Chambers@ec.gc.ca
Abstract
Inputs of nutrients (phosphorus, P, and nitrogen, N) to fresh waters can result in excessive aquatic plant growth, depletion of oxygen, and deleterious changes in abundance and diversity of aquatic invertebrates and fish. As part of a “National Agri-Environmental Standards Initiative”, the Government of Canada committed to development of non-regulatory environmental performance standards that establish desired environmental quality (for nutrients, sediments, pathogen and ecological flows) for agricultural streams. For P, efforts focus on identifying biological indicators and targets and, from these, P standards consistent with desired environmental condition. Our research into standards development employed an integrated approach consisting of analysis of existing data from forested and agricultural watersheds combined with experimental studies in networks of 10-15 streams.
Preliminary standards for P to maintain good ecological condition of agricultural streams in southern Ontario are 0.025 mg/L total P (TP) which should maintain suspended algae below ~1.4 µg/L chlorophyll a (chla) and benthic algae below ~50 mg chla/m2. Research is continuing on refining indicators for greater sensitivity and ease of measurement, and improving approaches for defining aquatic plant targets indicative of desired environmental quality.
Introduction
Addition of nutrients, in the form of phosphorus (P) and nitrogen (N), to aquatic ecosystems promotes excessive growth of algae and rooted aquatic plants, a condition known as eutrophication. The aim of this study was to develop and test approaches for setting standards for P and N, as agents of eutrophication, in order to protect and provide suitable conditions for a diverse community of aquatic organisms in Canadian agricultural streams. This study forms part of a “National
Agri-Environmental Standards Initiative” (NAESI), a program established by the Government of Canada to develop non-regulatory environmental performance standards to protect waters draining agricultural land.
Using data from southern Ontario and Quebec, Canada, we developed and tested several approaches for setting standards for P:
1. an empirical approach in which standards are based on a given percentile or other statistical descriptor of the dataset,
2. identification of critical junctures in the relationship between agricultural land cover in the watershed and P concentrations, and
3. identification of critical thresholds in relationships between aquatic plant abundance and P.
These analyses were undertaken using long-term (1971-2005) monitoring data from forested and agricultural watersheds, and new data (2005-2007) from 15
instrumented watersheds in agricultural and forested landscapes.
Methods
Three data sets were assembled for the Mixedwood Plains ecozone of southern Ontario and Quebec, Canada:
1. P concentrations from 117 stations on 101 streams (≤75 km2 in watershed area and <10% urban land cover), from the Ontario Provincial Water Quality Monitoring Network.
2. aquatic plant biomass (suspended and benthic algae, and rooted plants) and P concentrations for 55 stations on 43 streams and rivers in Ontario and Quebec, from provincial databases and published studies.
3. concurrent monthly measures of P and aquatic plant biomass (suspended, benthic and filamentous algae) from 15 streams in agricultural and forested landscapes.
Results and discussion
Concentrations of P in forested and agricultural watersheds in southern Ontario and Quebec, Canada ranged from 0.007-0.71 mg/L TP (station means) and 0.001-0.85 mg/L soluble reactive P (SRP). Aquatic plants were generally prolific, with summer maxima of 12 µg chla/L for suspended algae and 243 mg/m2 chla for benthic algae.
Up to 60% of the streambed was covered with benthic algae, rooted plants, or filamentous algae.
Comparison of empirical approaches for setting standards showed that two methods based on a given percentile of the data yielded similar results (Table 1). In the case of TP, empirical approaches yielded values of 0.020-0.026 mg/L for streams in southern Ontario. Plant abundance standards derived based on an empirical
approach were 1 µg chla/L for suspended algae and 59 mg chla/m2 for benthic algae.
Although this approach makes good use of available data, standards may be inflated due to inclusion of a high number of impaired streams.
Relationships between P and land cover were also evaluated for relevance in standards development: (1) linear regression was used to relate P concentrations or plant abundance to percent cropland cover in the watershed and the y-intercept was defined as the condition if zero cropland was present (Dodds and Oakes 2004), and (2) tree regression was used to identify a split in the X axis (i.e., percent cropland cover) which most significantly separated P concentration or plant abundance into two groups and a median was then calculated of the data in the lower range of cropland cover. These analyses resulted in values of 0.01 and 0.036 mg/L TP (Table 1). Although use of land cover versus nutrient relationships allows assessment as to whether specific P standards can be attained, the resulting standards are not linked to aquatic ecosystem health.
Table 1. Comparison of potential P standards developed for agricultural streams in Ontario, Canada using two approaches.
Parameter Units Empirical Approach Land Use Approach
Finally, analysis of aquatic plant data showed that suspended algae exhibited a linear response to TP whereas benthic algal abundance peaked at 0.040–0.050 mg/L TP and showed no response to higher concentrations while rooted plant abundance was not correlated with TP. To maintain aquatic plant growth below aesthetically and ecologically desirable limits of ~1.4 µg chla/L and 50 mg chla/m2 benthic algae, our data indicate that TP should not exceed 0.025 mg/L.
Research on approaches for setting nutrient standards is continuing and focuses on analyzing data for other regions of Canada, and testing the efficacy of indicators of aquatic plant abundance, composition or production as biological standards. These and other performance standards will be used in efforts to develop and promote the adoption of beneficial agricultural management systems and other practices that reduce environmental risks, and as benchmarks to measure progress toward identified goals.
References
ANZECC & ARMCANZ, 2000a. Australian and New Zealand guidelines for fresh and marine water quality. Volume 1. Australian and New Zealand Environment and Conservation Council, Agriculture and Resource Management Council of Australia and New Zealand.
ANZECC & ARMCANZ, 2000b. Australian and New Zealand guidelines for fresh and marine water quality. Volume 2. Australian and New Zealand Environment and Conservation Council, Agriculture and Resource Management Council of Australia and New Zealand.
Dodds, W.K. & Oakes, R.M., 2004. A technique for establishing reference nutrient
concentrations across watersheds affected by humans. Limnol. Oceanogr. Meth. 2, 333–
341.
USEPA (U.S. Environmental Protection Agency), 2000. Nutrient criteria technical guidance manual: Rivers and streams. Office of Water, Office of Science and Technology.
Washington, D.C.