Environmental Engineering Reference
In-Depth Information
(a)
1000
100
36
30
10
7.7
1
Marine
Freshwater
Terrestrial
(b)
10,000
970
1000
307
143
100
10
Marine
Freshwater
Terrestrial
FIGURE 2.4
(a) Molar carbon to nitrogen (C:N) and (b) carbon to phosphorus (C:P) ratios of autotrophs from
marine, freshwater, and terrestrial environments. Vertical line is the range of ratios for each environment.
Number associated with each bar is the mean ratio. Note the log scale. Marine and freshwater ratios are based on
samples of suspended particles filtered from water samples that represent a mixture of phytoplankton, other
organisms, and detritus. Terrestrial ratios are based on leaves and may not represent an entire plant, especially
those with woody structure.
(The means and ranges are values presented in
Sterner and Elser 2002.)
nutrient in lakes, but nitrogen is also needed in most cases to sustain increased primary
production (
Lewis and Wurtsbaugh 2008
). The island forests (
Figure 2.5c
) also exhibited
highest productivities in two of three cases with both nitrogen and phosphorus addition.
Because of the coupled nature of nutritional requirements, relief from one form of nutri-
ent limitation will often rapidly lead to limitation by a second nutrient. In addition, nutri-
ents can facilitate the uptake of other limiting nutrients. Nutrient additions to enclosures
in Lake Erie illustrate this colimitation and facilitated uptake (
North et al. 2007
).
Iron additions alone had little effect on the accumulation of phytoplankton biomass (a
surrogate for net primary production). Iron additions with other nutrients, however, were
associated with increased biomass (
Figure 2.5d
). Independent measurements of nutrient
status indicated the phytoplankton were strongly P-limited and moderately N-limited.
Adding iron and phosphorus helped overcome the N-limitation by facilitating the uptake
of nitrate, which requires Fe. Adding all three nutrients produced the greatest increase
