VII.  Results and Conclusions

Results

When critical loads values are subtracted from estimated mean annual load of titratable acidity, large differences are seen in the Appalachian Plateau (far west) and Southern Coastal Plain (southeast) regions of the state (Figure 8).  The results show that problems with stream acidification persist in these regions despite recent progress in emissions reductions.

Figure 8.  Difference maps showing total deposition in exceedance of critical loads

A striking similarity is seen when comparing MBSS stream chemistry results with these regional patterns in acid deposition (Figure 9).  Nearly all MBSS sites indicating stream acidification or acid sensitivity occur in areas experiencing total acid deposition in excess of critical loads.  This comparison verifies the accuracy of the deposition and critical loads models in predicting stream response.

Figure 9.  Acid Neutralizing Capacity values from the 1995-97 MBSS.

Conclusions

The results of this analysis suggest that critical loads continue to be exceeded in some areas of the state despite recent reductions in acid deposition.  The notable similarities between modeled deposition in excess of critical loads and measured stream response validate the deposition model.  Above average precipitation amounts in 1996 likely contributed to sulfate deposition in excess of critical loads in the Appalachian Plateau and Southern Coastal Plain regions.  Fish communities in affected areas exhibited low species richness and abundance.  Although Phase I results are encouraging, it is unlikely that complete implementation of CAAA Title IV will eliminate the acidification problems in all Maryland streams.

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