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Energy processing and ecosystem function in rivers essay example
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Energy processing and ecosystem function in rivers

Results

We are going to compare the litter’s breakdown of oak’s and alder’s leaves in three different stream groups: unimpacted by pollution, impacted by acid mine drainage and impacted by nutrient enrichments. To compare and see if there are significant differences between the different samples, a two-way analysis of variance (ANOVA) will be used with Minitab 15.

Comparison of the different leaves without considering the stream group

Figure 1 shows a difference between the mass loss of oak’s and alder’s litters. The analysis of the data on Minitab15 proved that there is a significant difference between mean values (two-sample t-test, t=2.99, DF = 16, p-value = 0.009). The litter mass loss is higher for the alder’s leaves than the oak’s leaves. For the oak’s leaves, there is a mass loss mean of 1.991g. For the alder’s leaves, the mass loss mean is 2.99g.

Comparison of the different stream groups without considering the leaf type

Figure 2 shows a difference of the litter’s mass loss mean for each stream group. According to Minitab 15, there is a significant interaction between stream with mine drainage and unimpacted stream on the litter’s mass loss (F = 107.18, DF = 2, 18, p < 0.001). There is also a significant interaction between stream with mine drainage and stream with nutrient enrichment on the litter’s mass loss (F = 107.18, DF = 2, 18, p < 0.001). There is a significant interaction between stream with nutrient enrichment and unimpacted stream on the litter’s mass loss (F = 107.18, DF = 2, 18, p < 0.001).
That means that the litter’s mass loss is significantly lower for the stream with mine drainage (mean = 1.5987g) and significantly higher for the stream with nutrient enrichment (mean = 3.347g). For the unimpacted stream, the litter’s mass loss mean is 2.533g, this is significantly lower than the stream with nutrient enrichment and higher than the stream with mine center48043200drainage.

Pairwise comparisons

Now that the effects of each group (stream and leaf type) separately have been compared, the totality of the data can be compared with a boxplot (Fig.3) and with the results of a two-way ANOVA (Fig. 4).
First, it is shown that for every stream group, the litter’s mass loss is higher for the alder than for the oak (Fig.3), these differences are significant for the unimpacted stream and for the stream with enrichment nutrient but according to Minitab 15 (Fig. 4), there is no significant interaction between alder and oak in a stream with mine drainage on the litter’s mass loss (p-value = 0.2119), oak’s leaf litter decomposition mean is 0.1676g lower than alder’s.
It is also shown that for the two leaf types, there is a significant difference between all the stream groups (Fig.4, p-value < 0.05). The nutrient enrichment stream being the one with the more massive litter mass loss and the mine drainage stream being the one the lower mass loss.

Discussion

Leaf litter mass loss represents the decomposition of the leaf litter. In streams, the leaf litter is decomposed by organisms. That is why there is a difference of the leaf litter mass loss depending on the stream group. With an acid mine drainage (AMR), the results showed that the leaf litter was less decomposed than a stream unimpacted by the pollution. When there is an AMR, the leaves have a lower pH and higher concentration of Fe and heavy metals (Pb, Hg, As) can be found in the stream and eventually on the leaves. These metals can be toxic for the macroinvertebrates such as decomposers leaving in the stream, but also for the non-acid-tolerant microorganisms. Because of the toxicity, some macroinvertebrates are more likely to die or to decrease their feeding, that can partially explain the low litter mass loss. Moreover, only acid-tolerant fungi can develop on the leaves because of the high pH. Fungi are important for the leaf litter primary decomposition (Pascoal & Cassio, 2004). Bacteria are also useful in the litter breakdown process once the leaves are partially decomposed. As there are less fungi and bacteria, the leaf litter won’t be decomposed as fast as in an unimpacted stream.

With a nutrient enrichment, the results showed that the leaf litter was more decomposed than in an unimpacted stream. Nutrient enrichment permits the leaf litter quality and the mineral nutrients availability to increase (Keuskamp et al. 2015). However, the litter’s breakdown in streams is especially influenced by the leaf quality and by environmental factors like the concentration of nutrients, in particular nitrogen and phosphorus (Pascoal & Cassio, 2004). These high concentrations of nutrients benefits microorganisms’ activities. As the microorganisms (fungi and bacteria) increase their role in the litter decomposition with the nutrient enrichment, the litter mass loss is higher in these conditions. Conversely, the nutrient enrichment can also affect the litter breakdown the other way “enrichment in one nutrient may decrease availability of another nutrient through plant uptake or immobilisation. This, in turn, may slow down decomposition, primary production, or both” (Keuskamp et al. 2015)

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The results also showed that the oak’s leaf litter decomposition was lower than the alder’s one. Previous studies (Ferreira et al. 2006) showed that the difference of decomposition between species of leaves are explained by the nitrate concentration, the Nitrate/Carbon ratio in them and their quality. Alder’s leaves have a high nitrate (and nutrient) content, whereas oak’s leaves are nutrient limited (Gulis et al. 2006). However, as the leaf litter is decomposed by organisms such as fungi

References

Ferreira, V., Gulis, V. & Graca, M.A.S. (2006). Wholestream nitrate addition affects litter decomposition and associated fungi but not invertebrates. Oecologia, 149. doi: 10.1007/s0042-006-0478-0
Gulis, V., Ferreira, V., Graca, M.A.S. (2006). Stimulation of leaf litter decomposition and associated fungi and invertebrates by moderate eutrophication: implications for stream assessment. Freshwater Biology, 51, 1655-1669. doi: 10.1111/j.1365-2427.2006.01615.xKeuskamp, J. A., Hefting, M. M., Dingemans, B. J. J., Verhoeven, J. T. A., & Feller, I. C. (2015). Effects of nutrient enrichment on mangrove leaf litter decomposition. Science of The Total Environment, 508, 402–410. doi: 10.1016/j.scitotenv.2014.11.092
Pascoal, C. & Cassio, F. (2004). Contribution of fungi and bacteria to leaf litter decomposition in a polluted river. Applied and Environmental Microbiology, 70, 9. doi: 10.1128/AEM.70.9.5266–5273.2004

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