Environmental Engineering Reference
In-Depth Information
concentrations of 500
m
gL
1
contrasting markedly with early industrial levels
of
100
m
gL
1
.
An understanding of nutrient flux in floodplain wetlands is confounded
by the unknown frequency of flooding and so level of hydrological and
sedimentary exchange between the wetland and the channel. The in-channel,
natural impoundments of lakes St Croix and Pepin overcome this limitation
and so provide a unique opportunity to assess nutrient flux using mass balance
approaches. Engstrom et al.(
2009
) undertook such mass balance analyses for
phosphorus on Lake Pepin. Phosphorus accumulation in the lake's sediments
increased 15-fold since 1830 from a baseline of 60 tonnes p.a. to 900 tonnes
presently, attributed evenly between increased loadings and increased phos-
phorus retention. Total phosphorus accumulation rate increased most rapidly
after 1940 and decreased after the 1970s, correlated with changing sediment
fluxes. Organic phosphorus increased to the present with maximum values in
the 1990s. This sedimentary phosphorus record was compared with diatom-
inferred total phosphorus that reflects principally the nutrient's bioavailable
concentration in the water column. Again, as in Europe, small eutraphentic,
planktonic forms including Stephanodiscus spp., Cyclotella meneghiniana and Cyclos-
tephanos invisitatus dominate the upper sediments that represent the post-1960s
period, some entering the record earlier than others. The inferred TP reinforces
the sediment measurements showing increased concentrations from early in
settlement, increasing markedly from the 1940s, and attaining maxima in
the uppermost layers. This record parallels that of some in the lowland River
Murray with declines in benthic taxa soon after settlement and a peak in
Aulacoseira subarctica in the early to mid 1900s. These lowland systems from
different continents, stimulated coincidentally by sediment and other releases
associated with industrial development from a range of sources, show a
remarkably similar record of change reinforcing the diatom palaeorecord as
a sensitive measure of eutrophication from industrialisation.
Salinity
Salts represent a less well-appreciated form of industrial pollution but are
recognised as a part of the cocktail released from the coal and textile indus-
tries. Diffuse pollution sources of salts are best known from saline seepage
associated with hydrological change and dryland salinisation through the
removal of vegetation cover or wetland or irrigation salinity. These have a long
history with evidence for salinisation impacting on productivity in the Tigris-
Euphrates, and Indus River catchments from early in settlement 4500 4000
years ago (Goudie
1993
). In the MDB too, salinity has a long history relative to
the duration of settlement. From as early as 1880, wetland salinity was evident,
as indicated by rises in the brackish water diatom taxa Amphora veneta,
Gyrosigma acuminatum and Tryblionella hungarica (Gell et al.
2005b
). While their
