|
Objectives
To provide an understanding of nutrient loadings and
water quality dynamics within Lake Waco, TIAER initiated
water quality monitoring of Lake Waco and all four major
tributaries flowing into Lake Waco in June 1996.
Methods
The monitoring data provide background information on
current nutrient conditions within Lake Waco and explore
the dynamics influencing eutrophication within the reservoir.
The stream and reservoir monitoring data have also been
used in calibrating computer models to evaluate the
impact of changing land management practices on stream
loadings and water quality within Lake Waco and in developing
nutrient targets for Lake Waco.
Results and Discussion
Our analysis demonstrates that in-lake and in-stream algal biomass varies as a
function of ambient PO4-P concentrations.
Additional tests of this functional relationship for both the Lake Waco and Bosque
River ecosystems have also revealed that algal biomass accumulates according to
a predictive, mechanistic model of resource-dependent growth with PO4-P
as the limiting resource. Given the level of documentation presented supporting
a cause and effect relationship between phosphorus availability and algal biomass,
PO4-P concentrations are a reasonable
indicator of ecosystem function and health for the Lake Waco-Bosque River watershed.
Specific targets defined in terms of average PO4-P
concentrations have a high probability of tracking ecosystem response to any future
restoration activities in the watershed.
An assessment of water quality within Lake Waco, in relation
to TCEQ screening levels for nutrients and chlorophyll-a, indicated concern or
potential concern for concentrations of NO2-N+NO3-N,
total-P, and chlorophyll-a. Although Lake Waco is not currently listed as a priority
reservoir for water quality issues, the reservoir appears to be nearing nutrient
and chlorophyll-a concentrations that could move it into a higher priority category
with regard to surface water quality concerns within the State of Texas.
Papers
Water Quality Modeling of Lake Waco Using CE-QUAL-W2 for Assessment of Phosphorus Control Strategies, This report documents the water quality modeling of Lake Waco that was performed under the USDA funded Lake Waco-Bosque River Initiative. Although the bulk of this report documents the model calibration process and underlying assumptions, the more meaningful outcome of the modeling exercise is the assessment of various control strategies with respect to target attainment. The assessment results represented the culmination of the modeling effort and when condensed into exceedence probability plots were effective tools in conveying the bottom-line to members of the Bosque River Advisory Committee (BRAC).
Nutrient Targets for Lake Waco and North Bosque River: Developing Ecosystem Restoration Criteria, The State of Texas has identified a number of water bodies as having potential water quality problems as a result of nutrient enrichment from point and nonpoint sources. In the Bosque River watershed, elevated levels of chlorophyll-a (CHLA) and nutrients have prompted the state to classify portions of the watershed as water quality impaired, and to place selected water quality segments on the Clean Water Act Section 303(d) list. In response to the listing of the Upper North Bosque River (Segment 1255) and the North Bosque River (Segment 1226) and in cooperation with stakeholders in the basin, water quality monitoring data and in situ nutrient bioassays were used to develop nutrient targets by answering the following questions:
What nutrient or nutrients limit aquatic primary production in the watershed?
What functional relationship(s), if any, exists between the limiting nutrient and primary production?
How do degraded water bodies compare to reference sites?
Characterization of a Central Texas Reservoir with Emphasis on Factors Influencing Algal Growth, Monitoring data collected between June 1996 and December 1999 were used to characterize water quality within Lake Waco with particular emphasis on factors influencing algal growth. A spatial analysis of surface water quality for Lake Waco established two different longitudinal patterns within the reservoir based on distance from major tributary inflows. For physical characteristics, such as conductivity and Secchi depth, riverine, transition, and lacustrine zones were identified along the northern and southern arms of the reservoir with increasing distance from major tributary inflows. For chemical and biological characteristics, such as chlorophyll-a (CHLA) and nitrogen (N) concentrations, a longitudinal gradient within the reservoir was followed based on proximity to either the northern or southern tributary inflows.
|
