Willem Goedkoop

Effects of deposit-feeder activity on bacterial production and abundance in profundal lake sediment.

Effects of the amphipod Monoporeia affinis, the oligochaete Tubifex tubifex and the chironomid Chironomus riparius on the production ([3H]-thymidine incorporation) and abundance (acridine orange direct counts) of sediment bacteria were studied in a series of microcosm experiments. Measurements were performed on the visually distinct sediment zonation generated by oxygen penetration and influenced by deposit-feeder activity. All three species at higher densities caused an increase in the depth of the light-colored surficial sediment layer in the microcosms. Bacterial production in surficial sediment increased by factors as high as 3.2× (Monoporeia experiment), 1.4× (Tubifex experiment), and 4.4× (Chironomus experiment) compared with controls. Physical disturbance of sediment through invertebrate activity was concluded to be the main causal mechanism for increases in bacterial production. Changes in bacterial abundance appeared to be zoobenthos species-specific, reflecting differences in feeding and/or foraging behavior of the animals. Bacterial abundance was negatively affected by mechanical stirring and by the activity of Tubifex tubifex, a subsurface deposit-feeder known to gain a large proportion of its energy demand from sediment bacteria. Monoporeia affinis and Chironomus riparius did not affect bacterial abundance; apparently their surficial feeding activity resulted in a compensation of bacterial losses. In subsurface sediment layers neither bacterial abundance nor production was affected by any of the three species.

Assessing the ecological integrity of boreal streams : A comparison of functional and structural responses

Functional (leaf litter breakdown) and structural (macroinvertebrate metrics) attributes of nine boreal streams showed predictable changes along a nutrient enrichment gradient. Of the functional metrics studied, the percentage leaf mass remaining after 118 days in coarse mesh bags was best correlated with the nutrient gradient. However, none of the functional metrics performed as well as the macroinvertebrate (structural) metrics studied here. Somewhat disconcerting was the finding that the importance of decomposition in coarse (k c values) and fine (k f values) mesh bags, and hence interpretation of the degree of impairment, changed with time (during the 118 day study). Our findings indicate that caution should be exercised if ratios of k-values for coarse and fine mesh bags are used to assess the ecological integrity of boreal streams. The poor performance of functional metrics in boreal streams may be attributed to slow rates of decomposition, resulting in the need for relatively long incubation times to increase power to detect change if/when it occurs. This conjecture was supported by the finding that the strongest correlation between leaf litter breakdown in coarse mesh bags and degree of impairment was noted after 118 days of incubation. Long study (incubation) time has, however, serious implications in biomonitoring since the risk of not recovering leaf-litter bags increases with time.

Factors Affecting Population Fluctuations of the Glacial Relict Amphipod Monoporeia affinis (Lindström) in Sweden's Largest Lakes

Abstract Factors affecting long-term (1982–2000) population densities of the glacial relict amphipod Monoporeia affinis were studied in Swedens three largest lakes. Monoporeia showed large population fluctuations in all three lakes, with conspicuous peaks in density occurring in Lakes Vänern and Mälaren. In Lake Vänern, amphipod densities showed highly significant relationships with spring maximum diatom biovolume at a 1-yr lag. The lack of relationship between diatom biovolumes and Monoporeia densities in L. Vättern is likely due to the larger depth and the lower nutrient content of this lake. In eutrophic L. Mälaren, summer hypoxia (< 4 mg O2 L−1) is likely an important regulating factor. Hypolimnetic temperature showed a clear periodicity with relatively warm deep water occurring between 1989 and 1994. Hypolimnetic temperatures in Vänern and Vättern were correlated with total solar irradiance. However, neither hypolimnetic water temperature nor diatom biovolumes correlated with the North Atlantic Oscillation winter index. We speculate that variations in temperature and nearbottom oxygen concentrations negatively affect population densities by acting on recruitment success (reproduction) and juvenile (young-of-the-year) survival.

Assessing microbial contamination and antibiotic resistant bacteria using zebra mussels (Dreissena polymorpha)

Aquatic pollution with faecal bacteria and subsequent consumption of contaminated water or food is a worldwide issue that causes severe health effects (e.g. meningitis, salmonellosis, dysentery). In addition, the excessive use of antibiotics in animal husbandry and human medicine has enhanced the selective pressure on pathogenic bacteria, further increasing human health risks and detrimental effects on natural microbial communities. This urges the need to monitor faecal contamination using a time-integrated approach, as grab water samples can miss pathogen peaks. We tested the ability of zebra mussels (Dreissena polymorpha) to take up and depurate faecal indicator bacteria such as Escherichia coli and intestinal enterococci. Furthermore, we quantified the frequency of antibiotic resistant bacteria in water and mussels both in controlled laboratory tests and under in situ conditions downstream of a sewage treatment plant (STP). Laboratory results show that bacterial indicators in mussels were 132 times higher than their concentration in water, and that mussels retained bacteria up to 2 days after pulse exposure. Field results show decreasing bacterial concentrations in both water and mussels downstream the STP, with maximum E. coli concentrations ranging 173-9 cfu mL-1 in water and 2970-330 cfu g-1 in mussels. Similarly, enterococci ranged 59-4 cfu mL-1 and 1450-240 cfu g-1 in water and mussels, respectively. High proportions of antibiotic resistant E. coli were found in mussels (72%) and water (65%), and slightly lower proportion of resistant enterococci was found in mussels (47%) and in water (34%). Moreover, 33% of the bacteria isolated from mussels were resistant to multiple antibiotics, which emphasizes that resistance is a common feature in surface waters and highlights the need for safe water management. Our results show that zebra mussels provide an efficient, time-integrating tool for quantifying faecal indicators, including resistant and multidrug resistant bacteria.

The effects of organic enrichment on leaf litter breakdown in three boreal streams

A number of bioassessment methods are eurrently used to assess the health and/or integrity of stream eeosystems. Most methods rely almost exclusively on struetural attributes of streams. For example, the use of taxon riehness is a metrie used in many bioassessment studies (REICE & WOHLENBERG 1993). A number of early studies eomparing the usefulness o f struetural and funetional aspeets for bioassessment eoncluded that metries such as ratios between functional groups were not better than measurements of eommunity strueture (RESH & JACKSON 1993). More reeently, it has been argued that biologieal proeesses (e.g. funetion) need to be eonsidered when developing bioassessment sehemes for biomonitoring (BUNN & DAVIES 2000, GESSNER & CHAUVET 2002). Sinee major flows of energy oeeur along the detritial pathways in stream eeosystems, leaf litter breakdown rates ean be a useful too! when diseerning patterns and meehanisms driving deeomposition in streams (HIEBER & GESSNER 2002). Moreover, functional ehanges supply additional information on the effeet of anthropogenie disturbanee on eeosystems funetion (REICE & WoHLENBERG 1993). The laek of knowledge about the response ofproeesses to various stresses makes identifying proeesses reaeting to specifie kinds o f stresses an important ehallenge ( GEssNER & CHAUVET 2002). In this study we investigated if leaf breakdown rates and/or the struetural eomposition (biotie indiees) ofthe maeroinvertebrate eommunity area better indieator of perturbation in stream eeosystems. Three boreal streams were seleeted to eompare responses of struetural and funetional metries to anthropogenie (nutrient enriehment) stress.