Modelling Catchment-Scale Responses to Climate Change - Climate Change Impacts on Freshwater Ecosystems - page 254

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Figure 10.5 INCA-N-simulated NO 3 concentrations and fluxes at the Bjerkreim River
outlet in 2030-49 and 2081-2100, based on the MPI and Had scenarios, respectively.
(From Kaste et al . 2006.)

to reductions in acid deposition (see Chapter 7). The increased N loading may
stimulate the growth of N-limited benthic algae and macrophytes along the river
channels and lead to undesirable eutrophication effects in the estuarine area.
Simulations made by the Fjord model indicate that primary production in the
summer in the estuary might increase by 15%-20% with the Had scenario. Since
this scenario does not entail any increase in NO 3 − fluxes during summer (Fig.
10.5), the production increase may be a result of a longer residence time of the
surface layer due to reduced freshwater inputs. It thus seems that the changes in
run-off patterns may have a greater effect on algal production than the changes
in nutrient conditions per se .
The linked-model approach presented here involved several sources of
uncertainty. Among these were uncertainties related to (i) scaling of input data;
(ii) climate and N deposition scenarios; (iii) model parameterization and
calibration; (iv) model structure/ability to simulate key processes and (v) transfer
of data with inherent uncertainties between models. All models involved proved
to be fairly robust in reproducing current data, but the number of processes which
have to be simulated to make predictions mean that the model results should be
regarded as possible outcomes and not forecasts, especially beyond 2050.
However, some of the responses predicted by the models are founded in
experimental and observational data. For instance, both laboratory- and large-
scale experiments have suggested that decomposition and N mineralization show
a faster response to a temperature increase than the corresponding N retention
processes, at least during an initial phase of the warming process (Kirschbaum