rate of sediment-induced storage loss in lakes and reservoirs
can be measured with a series of sedimentation or bathymetric surveys. Transects
and sampling points are often established perpendicular to the main axis of
tributary inflow or the main axis of the lake. Some base strata (original lake or
reservoir bottom) should be established to track the rate
of deposition. A
long pole may be used in shallow areas to measure sediment depth. For deeper
areas, sonar or a SCUBA diver can record sediment depth measurements.
Although measurements every year may not be needed, the same transects and
stations should be monitored periodically. Major changes in land use,
streambank erosion that could increase sedimentation should also be monitored.
tracer to estimate rates of sedimen-
McIntyre and Naney (1990) used the
Lake in Tennessee.
Transparency. An important and obvious property of water is its transparency.
The transparency of water to light is critical for aesthetic enjoyment, sight-feeding
fish, and recreational uses such as swimming. Transparency decreases as algal and
dissolved and particulate matter increase water column turbidity. The
Secchi disk is an easy, low-cost measure of transparency that provides a rough
measure of trophic state. Measured periodically throughout the year, Secchi disk
readings can be tracked along with other seasonal changes related to mixing, alga1
succession, and decay, and the changes in suspended sediment due inflows or
turbidity such as suspended sediment, detritus, dissolved
material, and color, and the light attenuation properties of different types of algal
cells can impair the interpretation of Secchi disk data and other trophic state
Turbidity. The reduced transmission of light due to scattering or absorption by
suspended solids such as silt and clay particles can be measured by several types
of instruments, including the
and spectrophotometer. Vertical
illumination may be measured by the submarine photometer. Methods are
available in APHS (1980) and Lind (1985).
Phosphorus. The choice in monitoring phosphorus constituents is based on the
source of the pollution problem and the expected advantage of tracking additional
variables. Monitoringortho-phosphate is a basicconstituent since it represents the
fraction available for plant growth. Total phosphorus is useful for comparison
with other measures of trophic state, the development of nutrient budgets, and its
application to lake modeling.
Nitrogen. Nitrogen monitoring generally accompanies phosphorus monitoring
for surface water studies. Many eutrophication problems have been linked either
in part or wholly to nitrogen. Total
nitrogen (TKN) is a measure of
organic nitrogen and ammonia and is typically a large constituent. Ammonia
nitrogen, while often in low concentration, may exceed 10
in the anaerobic
hypolimnion of an eutrophic lake. Nitrate is also useful to determine total nitrogen
and for an assessment of the likelihood of blue-green algae.
Level II Water Quality
The monitoring of treatment program effectiveness when variability is high or
when the change to be detected in a variable is subtle requires more detail and
careful selection of variables, explanatory variables, and monitoring design.
Objectives for level II monitoring include detecting trends, impacts, or causality
with water quality variables or pollutant loads.