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Ecological Study:
Nutrients in Utah’s Waters

The Utah Division of Water Quality conducted a study in 2010 to evaluate the ecological impacts of nutrient additions from POTWs on the State’s streams and rivers. The study was conducted on receiving waters above and below the discharges of eight mechanical treatment plants and one lagoon system. The Division studied these waters above and below discharges for changes in:

To extrapolate these findings to all of Utah’s waters a water quality model is being developed from these sites to determine what the effects of nutrient additions, or removals, are on other waterbodies.

Because many of the State’s POTW receiving waters are near population centers they are already nutrient enriched from urban or agricultural sources. The Division also surveyed 17 least disturbed streams to determine how streams function with minimal human disturbance as a reference benchmark.

The Division of Water Quality is still in the process of analyzing and interpreting the results from the 2010 field season. For questions about the 2010 Nutrient Criteria Ecological Study contact Mike Shupryt.

The Nutrient Criteria Ecological Study was conducted on the following waterbodies:

Box Elder CreekBrigham City WWTP
Dry CreekSpanish Fork City WWTP
Little Bear RiverWellsville Lagoons
Malad RiverTremonton City WWTP
Price RiverPrice River Water Improvement District
San Pitch RiverFairview City WWTP
San Pitch RiverMoroni City WWTP
Silver CreekSnyderville Basin-Silver Creek Water Reclamation Facility
Weber RiverOakley City WWTP

Stream Metabolism

Whole stream metabolism measures the ratio of primary production (plants and algae) to respiration (microbes, insects, fish, plants and algae). Stream metabolism can be measured through daily changes in dissolved oxygen streams and rivers. During the day plants and algae produce excess oxygen and saturate the water. During this time primary production (therefore oxygen levels) are greater than respiration (use of oxygen by organisms). At night primary production is halted and respiration is the major metabolic function. Stream metabolism can be measured by theses daily changes in oxygen concentrations in the water column. Increased nutrients can alter the sources of energy entering the stream shifting the ratio of primary production to respiration. These changes often manifest themselves as increased fluctuations in daily dissolved oxygen. This may result in very low night time dissolved oxygen concentrations that are harmful to aquatic life.

Nutrient Limitation

Growth of primary producers (plants and algae) in streams is usually limited by the available nutrients in the water. Increases in important nutrients, like nitrogen (N) and phosphorus (P), can lead to rapid increases in primary production and increase the overall available energy in a system. We used growth plates spiked with nutrient enriched (N, P & N+P) agar to evaluate the effects of added nutrients on algal growth. This can help determine if a particular waterbody needs to have more restrictive nutrient criteria for nitrogen, phosphorus or both.

Ecosystem Function

Some in stream responses to nutrients are difficult to quantify. One of these is the response of microbes (bacteria and fungi) to nutrient additions. Microbes can be extremely variable in space and time making them very difficult to quantify in an efficient manner. One way to remedy this problem is to measure an important function in stream ecosystems that microbes are involved in. We measured decomposition rates of leaves and wood in streams. Microbes are the main decomposers in aquatic systems and release vital energy and nutrients stored as indigestible plant materials and make them available to other organisms. Along with primary production, the decomposition of leaves and wood washed from upstream are the two major sources of energy in stream ecosystems. From these decomposition rates we can evaluate the affects of increased nutrients on microbial activity in streams.

Water Chemistry and Quality

POTW discharges contain a number of dissolved chemicals that affect their receiving waters. This study is most concerned with the nutrients, nitrogen (N) and (P), in POTW discharges and how streams react to these additions. We measured nutrients upstream of POTWs, in the POTW discharges and at multiple stations downstream of the discharge. We monitored two stations above discharges to determine how ambient nutrient concentrations were naturally changing. We then monitored two or more stations downstream of the POTW discharge to see how the addition of nutrients changed the ambient dynamic. We could determine if the stream was able to process and retain nutrients or if the excess nutrients passed downstream, possibly to a larger river or lake. We were also able to use these background concentrations of nutrients and compare that to a number of in-stream measures such as: algal abundance, organic matter storage, water temperature, dissolved oxygen, turbidity, etc.

Organic Matter Storage

Organic matter is all the carbon based material in a stream. Organic matter is supplied to a stream in numerous ways such as terrestrial wood and leaves, soil erosion decomposition of plants, algae and animals and primary production. One way to measure how energy and carbon are stored within a system is to look at all the organic matter stored in the stream at one point in time. Increased nutrient loading from POTW discharges can increase whole stream productivity and increase the total amount of carbon in a system. Organic matter sampling is a way to quantify the total increase in productivity.

Macroinvertebrate and Fish Communities

Macroinvertebrate and fish community assessments are used by many States to determine the health of stream ecosystems. Certain species of macroinvertebrates and fish are less tolerant to different forms of pollution and by sampling the entire community they can provide valid information about stream health. Biologic communities are useful forms of assessment because they reflect the cumulative stressors upon the stream over the length of each organisms life, which may be weeks to years. The Division sampled macroinvertebrate and fish communities above and below the POTWs to examine the affects of increased nutrients on biologic communities.



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