Monitoring Program Design - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 311

This is because most of the problems experienced in lagoons are related to
eutrophication, nutrient enrichment/high primary productivity: unusually high
organic carbon and nutrient concentrations, particularly after accumulation periods,
high pH during productive season, large amount of suspended matter, and oversat-
uration with oxygen in productive layers. But due to the highly dynamic nature of
some lagoons, it is very difficult to monitor nutrient fluxes. The effect of most
important kinetic processes explained in Chapter 4 varies significantly between the
intermediate mixing zone and the rest of the lagoon, and these variations create
problems for effective monitoring.
Many examples show that morphology of the area and local hydrological con-
ditions are important factors affecting behavior of nutrients. Inputs of nutrients can
be severely influenced by tidal phenomena. Given the above considerations, it seems
there is no universal, simple approach to monitoring of nutrients. It is unrealistic to
develop a general monitoring strategy for nutrient exchange. In the case of riverine
lagoons, gross nutrient flux from rivers should be determined. Satisfactory nutrient
budget will require many cruises and sampling stations, which is often unrealistic
in the long term. A short-term, intensive project is recommended; modeling will
help plan the special scheme of measurements.
Special methodology is often necessary in the case of lagoons, due to their
specific nature. For example, the analytical techniques utilized in measuring eutroph-
ication parameters in marine areas or fresh waters are sometimes not applicable to
lagoons, due to factors such as intermediate salinity, possibility of the presence of
humid substances, differing water color, and presence of a large amount of suspended
material. A further point to be considered is that lagoons are often remote, at a great
distance from laboratories. Prior to analysis samples, which are usually gathered from
a small research boat, must be preserved taking into consideration long distances and
time.
Analyses of nutrients are based on spectrophotometric methods, so water color
is an important consideration. Water color may vary in lagoons due to, for example,
local events or the absence or presence of humic substances. Interpretation of results
must therefore consider both temporal and spatial variability in water color. Results
from spectrophotometric analysis will likewise be affected by the presence of sus-
pended matter, which may be present in lagoons, but is seldom encountered in the
water column in the open sea. Filtering or centrifugation (in the case of ammonia
determination) is therefore necessary.
There is usually a need for immediate analysis, which could be problematic in the
case of isolated lagoons. Strictly followed preservation methods are necessary for some
chemical measures, although immediate analysis is definitely preferred. If this is not
a possibility, samples should be kept cool or frozen. In the case of biogenic salts,
samples can be stored safely up to 6 h at 0

° C, and for a longer time if stored below

-20 C. Preservation methods with addition of chemicals (chlorophorm, mercury,

sulfuric acid), which have been used historically, are not recommended.
Automatic analytical methods may not be possible in a dynamic lagoon subject to
varying water properties and concentrations, a typical feature of lagoons. Analysts must
carefully consider calibration in such cases. Concentrations beyond the calibration

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