EFFECTS OF STREAM DEGRADATION ON ECOSYSTEM FUNCTION ARE MEDIATED BY LOCAL MICROBIAL AND MACROINVERTEBRATE LEAF LITTER PROCESSING

Riparian areas are fundamental to aquatic ecosystems by regulating temperature and light regimes, and providing allochthonous subsidies critical to the survival of aquatic and terrestrial species. On a global scale, increased rates of anthropogenic disturbance from agricultural activities and urbanization have caused the degradation of aquatic habitats. As a result, billions of dollars have been spent on stream restoration projects to protect aquatic resources; however, fundamental ecosystem processes like litter decomposition are rarely addressed. We conducted a litterbag experiment in a degraded high desert stream proposed for large-scale restoration to test the effects of reach location, canopy cover, and temperature on the rates of leaf litter breakdown attributed to microbial activity and macroinvertebrate shredders. Results from coarse mesh litterbags indicated that total leaf breakdown rates per degree-day were significantly faster in upstream, less degraded reaches, associated with higher abundance of shredders. In contrast, the main driver of leaf mass loss due to microbial activity in fine mesh litterbags was water temperature, which was significantly warmer in downstream reaches. Location effects, including temperature differences between upstream and downstream reaches, also depended on canopy cover and leaf species. Overall, the relative proportion of leaf mass loss attributed to microbial activity increased with increasing cumulative degree-days, while leaf mass loss attributed to shredders decreased. Reduced leaf processing rates by shredders in the degraded downstream reaches could further affect the timing and availability of suspended food resources to other detritivore and higher-level consumers downstream. These shifts in microbial and shredder-mediated leaf litter processing could have bottom-up effects via heterotrophic energy pathways, especially in degraded streams subject to warming. Furthermore, the significant variation in litter decomposition we observed underscores the importance of measuring ecosystem function across multiple scales within a given stream in order to assess relative levels of degradation and guide future restoration efforts

The professionalisation of the Netherlands armed force

The fall of the Berlin Wall and the end of the Cold War led in 1991 to the decision to gradually reduce and restructure the Netherlands armed forces. It was process consisting of dozens of reorganisations. The idea was that the reorganisation and reduction would go hand in hand, not only operationally but also financially. Firstly, only one in three men were actually still called up in order to fulfil conscription duties lasting more or less a year. There was one more condition for the transformation: no increase in the personnel budget was permitted. The recruitment results were good for the first few years. As of 1996 the economic boom began. Recruitment came under pressure and the results started to decrease. The first crucial success factor concerning recruitment is the image of the armed forces. In view of the difficult labour market, salary, accommodation, training facilities and career opportunities must be competitive. Experience has shown that manning the armed forces depends on the position of the Defence on the labour market. This means that the armed forces need to learn to work together and to interact with other players on the labour market and to adapt to the labour market dynamics. This also means that the entire organisation needs to be adapted to this new position

Assessing the impacts of human-induced degradation on stream ecosystem function

Riparian vegetation provides many ecosystem services to streams, especially as a source of organic matter critical for many aquatic organisms. Kimball Creek (De Beque, CO) is a heavily degraded stream in which loss of riparian vegetation and altered hydrologic regimes may have caused a decrease in litter resources and increased light penetration, inducing a shift from an allochthonous based system to an autochthonous one. In two stream reaches, “reference” and “degraded”, tiles were submerged in riffle habitat to estimate algal growth. While benthic algae biomass was not significantly different between reaches, chlorophyll a was highest in the reference reach after four weeks submergence. In addition, a leaf pack experiment was conducted using box-elder and willow to estimate litter decomposition over time. As expected, box-elder decayed significantly faster than willow in both reaches. Interestingly, box-elder decayed faster in the degraded reach, while willow decayed at the same rate in both the reference and degraded reaches. Future research is needed to further investigate the effects of riparian loss on stream food web and bottom-up pathways in this and other degraded streams

Examining the effects of riparian disturbance on litter decomposition in a degraded stream

In forested streams, organic matter imported from riparian vegetation is a primary source of energy, especially for macroinvertebrate shredders. In western Colorado, Kimball Creek is a degraded stream in which loss of riparian vegetation may have decreased litter inputs, altering shredder abundance and therefore litter decomposition rates. In two open canopy and two shaded stream reaches, leaf pack experiments using box-elder (Acer negundo) and gamble oak (Quercus gambelii) were conducted to determine litter decomposition rates. In addition, macroinvertebrates collected from leaf packs were used to investigate potential differences in shredder abundance and diversity between the four study reaches. Research is ongoing and may provide insight into understanding the effects of human-induced degradation on stream ecosystem function