2.2 Where, What, and When to Sample
41
tend to be N limited. Land clearing, agricultural land uses, sewage treatment
discharge, and atmospheric deposition can all result in high loadings of N to
coastal zones. Excessive N inputs can contribute to a range of impacts, including enhanced algal blooms, decreased distribution of seagrass habitat, and
decreased dissolved oxygen (DO) concentration (Valiela et al. 1992, Nixon 1995,
Borum 1996, Bricker et al. 1999, Kopp and Neckles 2004). Because of human
population growth and urban development in coastal areas, there is substantial potential for increased N loading to coastal ecosystems. Atmospheric
deposition of N contributes to that load but is generally not the major source
of estuarine N. AQRVs for protection of estuarine ecological conditions are
beyond the scope of this book. Recommendations for monitoring estuaries and
other coastal areas are therefore not addressed.
There is no clear-cut selection of chemical parameters to include in a study
of potential eutrophication of lake or stream water. A variety of measurements
can be useful (Table 2.3). In general, measures of N, P, and chlorophyll a are
of greatest importance. We recommend, at a minimum, that water samples
be analyzed for total N, NO 3
− , NH 4
+ , total P, soluble reactive phosphorus (SRP),
and chlorophyll a. In addition, dissolved organic N (DON) may be of interest.
The measurement of SRP is intended to reflect the forms of P in surface waters
that are most readily available to aquatic biota. Nevertheless, P forms are to
some extent interchangeable within the water column and stream/lake sediment. Therefore, measured total P (which includes both soluble and particulate
forms) is also of interest in evaluating potential nutrient limitation and growth
responses. In general, NH 4
+ and NO 3
− are considered to be biologically available forms of N. Nevertheless, DON may be converted to NH 4
+ and NO 3
− or used
directly by some primary producers. Therefore, measured total N is also of interest. Additional physicochemical parameters that can be useful in evaluation
of nutrient status include iron (and perhaps other metals); Si (lakes only); DO;
total suspended solids (TSS); turbidity; Ca 2+ ; total Al; and Secchi depth (a physical, rather than a chemical, measurement). Iron, Ca 2+ , and Al can bind to P and
influence its cycling between sediment and water and also its bioavailability.
Silicon can be limiting or colimiting, along with P and N, to diatom productivity. It can also provide information regarding groundwater inflow to a lake.
High productivity in response to nutrient enrichment can lead to reduction in
DO as primary producers die and decay, consuming oxygen (O 2 ) through microbial respiration. This effect is generally associated with rather extreme eutrophication, well above the levels that might be expected to occur in response
to atmospheric deposition inputs to freshwaters in the United States. The TSS
concentration is useful because eroded sediments, especially the smaller claysize particles, can be relatively enriched in adsorbed P, depending on local geology and land use. Thus, eroded sediments contribute to the total P in surface
waters, especially in streams during high-flow periods. At locations where the
41
tend to be N limited. Land clearing, agricultural land uses, sewage treatment
discharge, and atmospheric deposition can all result in high loadings of N to
coastal zones. Excessive N inputs can contribute to a range of impacts, including enhanced algal blooms, decreased distribution of seagrass habitat, and
decreased dissolved oxygen (DO) concentration (Valiela et al. 1992, Nixon 1995,
Borum 1996, Bricker et al. 1999, Kopp and Neckles 2004). Because of human
population growth and urban development in coastal areas, there is substantial potential for increased N loading to coastal ecosystems. Atmospheric
deposition of N contributes to that load but is generally not the major source
of estuarine N. AQRVs for protection of estuarine ecological conditions are
beyond the scope of this book. Recommendations for monitoring estuaries and
other coastal areas are therefore not addressed.
There is no clear-cut selection of chemical parameters to include in a study
of potential eutrophication of lake or stream water. A variety of measurements
can be useful (Table 2.3). In general, measures of N, P, and chlorophyll a are
of greatest importance. We recommend, at a minimum, that water samples
be analyzed for total N, NO 3
− , NH 4
+ , total P, soluble reactive phosphorus (SRP),
and chlorophyll a. In addition, dissolved organic N (DON) may be of interest.
The measurement of SRP is intended to reflect the forms of P in surface waters
that are most readily available to aquatic biota. Nevertheless, P forms are to
some extent interchangeable within the water column and stream/lake sediment. Therefore, measured total P (which includes both soluble and particulate
forms) is also of interest in evaluating potential nutrient limitation and growth
responses. In general, NH 4
+ and NO 3
− are considered to be biologically available forms of N. Nevertheless, DON may be converted to NH 4
+ and NO 3
− or used
directly by some primary producers. Therefore, measured total N is also of interest. Additional physicochemical parameters that can be useful in evaluation
of nutrient status include iron (and perhaps other metals); Si (lakes only); DO;
total suspended solids (TSS); turbidity; Ca 2+ ; total Al; and Secchi depth (a physical, rather than a chemical, measurement). Iron, Ca 2+ , and Al can bind to P and
influence its cycling between sediment and water and also its bioavailability.
Silicon can be limiting or colimiting, along with P and N, to diatom productivity. It can also provide information regarding groundwater inflow to a lake.
High productivity in response to nutrient enrichment can lead to reduction in
DO as primary producers die and decay, consuming oxygen (O 2 ) through microbial respiration. This effect is generally associated with rather extreme eutrophication, well above the levels that might be expected to occur in response
to atmospheric deposition inputs to freshwaters in the United States. The TSS
concentration is useful because eroded sediments, especially the smaller claysize particles, can be relatively enriched in adsorbed P, depending on local geology and land use. Thus, eroded sediments contribute to the total P in surface
waters, especially in streams during high-flow periods. At locations where the