Benthic fauna in a series of lakes displaying a gradient of pH

The benthic fauna was examined in a series of four isolated headwater lakes, displaying a pH gradient of 5.4–7.0. A slight reduction in number of taxa present occurred below pH 6, with the fauna below 3 m dominated by the Diptera. Although epibenthic gastropods were rare, in contrast with European studies, Amphipoda, Ephemeroptera and Pisidium were common in the least buffered lake, which experiences spring pH values as low as 4.7. There were little relation between the pH or alkalinity, and the abundance, and biomass of the fauna at depths greater than 3 m. However, biomass of the littoral fauna increased significantly in the lakes with lower pH, as a result of an increase in large littoral species normally susceptible to fish predation.     

Benthic community response (primarily Chironomidae) to nutrient enrichment and alkalinization in shallow,soft water humic lakes

A comparison of the benthic fauna found in two shallow lakes in the New Jersey Pinelands (USA) illustrated the impact of elevated pH and nutrients caused by residential and agricultural disturbance on a naturally acidic, poorly buffered aquatic environment. Detailed community analysis suggested that change in community composition was a better indicator of response to disturbance than biological diversity indices. Chironomidae (insecta) were the predominant components of the benthic macroinvertebrate assemblage of both undisturbed Oswego Lake (low pH, low nutrients) and Nescochague Lake (fluctuating pH, elevated nutrients). The genera Procladius, Tribelos, and Pagastiella dominated Oswego Lake, where as Zalutschia zalutschicola, Procladius, Dicrotendipes, and Tanytarsus dominated Nescochague Lake. Glyptotendipes was a common and unique member of the Nescochague Lake assemblage. Cluster analysis indicated that the chemical differences between lakes were the most important community determinants, although, within each lake, depth and substrate affected the local communities. Oswego Lake exhibited a depauperate nonchironomid benthic fauna typical of low nutrient, acid lakes. In turn, Nescochague Lake exhibited an enriched nonchironomid fauna including mollusks and planaria which were not found in Oswego Lake.     

大型水电站对河流底栖藻类群落的影响

2004年9月—2007年6月,对古夫河受大型水电站影响的GF04样点及高岚河的参照样点GL03进行逐月采样,研究了大型水电站对古夫河底栖藻类的影响.结果表明：研究期间,两样点主要理化指标差异均不显著（P>0.05）;两样点水动力学差异显著（P<0.05）,研究期间GL03样点基本处于缓流状态,其季节变化显著（P<0.05）,而GF04样点由于受水库放水影响,采样期间60%以上时间处于急流状态,没有明显的季节节律,说明水动力学及生境的变化是影响研究区底栖藻类群落的重要因素;群落相似性以及非着生型硅藻、直立型硅藻、有柄型硅藻的相对丰度在两样点间的差异显著,可很好地反映大型水电站不定期放水对河流生态系统的影响.     

Bacteria and algae in stream periphyton along a nutrient gradient

1. Stream riffles in southern Ontario and western Quèbec were sampled for biomass (58 stations from 51 streams) and production (22 stations from 21 streams) of algae and bacteria in periphyton to test the hypothesis that bacteria in benthic biofilms compete with algae for nutrients. 2. Algal and bacterial biomass were positively correlated, as were algal and bacterial production. Bacterial production was also positively correlated to algal and bacterial biomass, but the relationship was not significant. The ratio of algal to bacterial biomass did not vary with nutrients whereas algal production tended to increase with nutrients more rapidly than bacterial production. 3. Instream nitrogen concentrations explained 38–58% of the variability in algal biomass and production. Bacterial abundance explained an additional 9–29% of the residual variance in algal production and biomass. However, the relationship between bacterial abundance and algal production and biomass, once nutrients were taken into account, was positive, in contrast to the predicted effect of competition. 4. Hence, we reject our original hypothesis that bacteria in biofilms compete with algae for nutrients and instead suggest that bacteria and algae in biofilms coexist in an association that offers space and resources to sustain production of both groups of organisms.     

Changes in coral microbial communities in response to a natural pH gradient

Surface seawater pH is currently 0.1 units lower than pre-industrial values and is projected to decrease by up to 0.4 units by the end of the century. This acidification has the potential to cause significant perturbations to the physiology of ocean organisms, particularly those such as corals that build their skeletons/shells from calcium carbonate. Reduced ocean pH could also have an impact on the coral microbial community, and thus may affect coral physiology and health. Most of the studies to date have examined the impact of ocean acidification on corals and/or associated microbiota under controlled laboratory conditions. Here we report the first study that examines the changes in coral microbial communities in response to a natural pH gradient (mean pH_T 7.3–8.1) caused by volcanic CO₂ vents off Ischia, Gulf of Naples, Italy. Two Mediterranean coral species, Balanophyllia europaea and Cladocora caespitosa, were examined. The microbial community diversity and the physiological parameters of the endosymbiotic dinoflagellates (Symbiodinium spp.) were monitored. We found that pH did not have a significant impact on the composition of associated microbial communities in both coral species. In contrast to some earlier studies, we found that corals present at the lower pH sites exhibited only minor physiological changes and no microbial pathogens were detected. Together, these results provide new insights into the impact of ocean acidification on the coral holobiont.     

Distribution of benthic algae and macroinvertebrates along a thermal stream gradient

The distribution and abundance of benthic algae and macroinvertebrates were examined along a natural thermal gradient formed by hot springs in Little Geysers Creek, Sonoma Co., California, USA. Maximum water temperatures ranged from 52 °C at the uppermost station to 23 °C at a station 400 m downstream. Benthic chlorophyll a decreased exponentially from 2.5 g m^–2 at 52 °C to less than 0.1 g m^–2 at 23 °C, a pattern of decline also exhibited by algal phaeophytin. Blue-green algae dominated at higher temperatures but were replaced by filamentous green algae and diatoms at lower temperatures.Macroinvertebrates were absent at temperatures 45 °C; the highest density (> 150 000 m^–2, mainly Chironomidae) occurred at 34 °C, whereas biomass was highest (4.6 g m^–2, as dry weight) at 23 °C and species richness (15 species) was highest at 27 °C. The two predominant macroinvertebrate populations (the midge Tanytarsus sp. and the caddisfly Helicopsyche borealis) occurred at sites that were several degrees below their lethal thermal threshold, suggesting that a temperature buffer is maintained.     

Nutrient limitation of algal periphyton in streams along an acid mine drainage gradient

Metal oxyhydroxide precipitates that form from acid mine drainage (AMD) may indirectly limit periphyton by sorbing nutrients, particularly P. We examined effects of nutrient addition on periphytic algal biomass (chl a), community structure, and carbon and nitrogen content along an AMD gradient. Nutrient diffusing substrata with treatments of +P, +NP and control were placed at seven stream sites. Conductivity and SO₄ concentration ranged over an order of magnitude among sites and were used to define the AMD gradient, as they best indicate mine discharge sources of metals that create oxyhydroxide precipitates. Aqueous total phosphorous (TP) ranged from 2 to 23 μg · L^?1 and significantly decreased with increasing SO₄. Mean chl a concentrations at sites ranged from 0.2 to 8.1 μg · cm^?2. Across all sites, algal biomass was significantly higher on +NP than control treatments (Co), and significantly increased with +NP. The degree of nutrient limitation was determined by the increase in chl a concentration on +NP relative to Co (response ratio), which ranged from 0.6 to 9.7. Response to nutrient addition significantly declined with increasing aqueous TP, and significantly increased with increasing SO₄. Thus, nutrient limitation of algal biomass increased with AMD impact, indicating metal oxyhydroxides associated with AMD likely decreased P availability. Algal species composition was significantly affected by site but not nutrient treatment. Percent carbon content of periphyton on the Co significantly increased with AMD impact and corresponded to an increase in the relative abundance of Chlorophytes. Changes in periphyton biomass and cellular nutrient content associated with nutrient limitation in AMD streams may affect higher trophic levels.     

河流着生藻类多样性对城镇化的响应——以深圳市为例

着生藻类是河流生态状况的重要指示生物,然而关于城镇化对着生藻类多样性影响的研究还较缺乏。基于深圳市9条主要河流74个样点2020年雨、旱季的调查数据,对比了城区、郊区河流样点的着生藻类α、β多样性。两次调查共鉴定出着生藻类301个分类单元,其中硅藻门种类最多。谷皮菱形藻(Nitzschia palea)、隐头舟形藻(Navicula cryptocephala)、平庸菱形藻(Nitzschia inconspicua)等污染指示种在城区组相对丰度更高,而清洁指示种微小曲丝藻(Achnanthidium minutissimum)在郊区组相对丰度更高。城镇化对着生藻类物种丰富度、香农维纳多样性指数、Pielou均匀度指数等α多样性指数均无显著影响,但对着生藻类群落结构有显著影响。城区组样点的着生藻类β多样性(用主坐标分析质心指示)低于郊区组,城区组与郊区组藻类β多样性差异在旱季更为显著。两组样点的藻类β多样性差异主要来源于物种周转组分。与城区组着生藻类群落显著相关的环境因子包括总氮、高锰酸钾指数、电导率、pH、浊度和水深,而与郊区组着生藻类群落显著相关的是总氮、溶解性无机磷和电导率。研究...     

Benthic algal biomass and productivity in high subarctic streams,Alaska

Year-round measurements of the standing crop of epilithic algae (as chlorophyll a concentration) in two streams — one second and one fourth order (map scale 1:63 360) — in interior Alaska (64°–65° N) were only about one tenth that reported from streams of temperate North America. Cell densities in these streams, however, were similar to those in comparable temperate streams. Year-round domination of the benthic flora by very tiny diatoms (Achnanthes spp.) may explain the apparent disparity between low chlorophyll a content and nearly average cell densities. Chlorophyll a standing crop in a more alkaline groundwater-fed stream, however, was higher and within the range of similarly sized temperate streams. Maximum chlorophyll a standing crop varied positively with alkalinity in 5 clear-water streams where standing crop was measured on natural or artificial substrates. Seasonal mean concentrations of sestonic chlorophyll a (used as estimates of benthic algal chlorophyll a standing crop) varied directly and significantly with alkalinity among ten clear-water streams; and, with total phosphorus among 8 of 10 clear-water and 5 brown-water streams studied. During the summer, when there is little darkness, gross primary productivity (as estimated by the diurnal dissolved-oxygen method) was similar to that of northern temperate streams. Gross primary productivity was also seen to vary directly with alkalinity in 5 clear-water streams of this region.U.S. Fish and Wildlife Service     

The role of light availability and herbivory on algal responses to nutrient enrichment in a riparian wetland,Alaska

We investigated how the relative availability of solar radiation in the presence or absence of grazing alters the ability of benthic algae to respond to nutrient enrichment in an Alaskan marsh. We used a factorial mesocosm experiment that included nutrient enrichment (enriched or control), grazing (grazed or ungrazed), and light (unshaded or shaded) to simulate shading by macrophytes early and late in the growing season, respectively. We found stronger effects of grazers and nutrients compared to light on benthic algal biomass and taxonomic composition. Algal biomass increased in nutrient‐enriched treatments and was reduced by grazing. Shading did not have an effect on algal biomass or taxonomic composition, but the concentration of chl a per algal biovolume increased with shading, demonstrating the ability of algae to compensate for changes in light availability. Algal taxonomic composition was more affected by grazer presence than nutrients or light. Grazer‐resistant taxa (basal filaments of Stigeoclonium) were replaced by diatoms (Nitzschia) and filamentous green algae (Ulothrix) when herbivores were removed. The interacting and opposing influences of nutrients and grazing indicate that the algal community is under dual control from the bottom‐up (nutrient limitation) and from the top‐down (consumption by herbivores), although grazers had a stronger influence on algal biomass and taxonomic composition than nutrient enrichment. Our results suggest that low light availability will not inhibit the algal response to elevated nutrient concentrations expected with ongoing climate change, but grazers rapidly consume algae following enrichment, masking the effects of elevated nutrients on algal production.     

The effects of nutrient,pH and herbicide levels on algal growth

Growth inhibition of algae increased as herbicide concentrations increased, particularly with prometryn and fluometuron. However, picloram had no effect on algal growth while dinoseb inhibited only Lyngbya. There were no differences in growth rate of algae treated with different levels of potassium or phosphorus. High levels of calcium or magnesium increased growth rate of the algae tested. High levels of nitrogen or pH increased growth rates except when combined with prometryn or fluometuron.     

Relative strengths of benthic algal nutrient and grazer limitation along a lake productivity gradient

The relative effects of nutrients and herbivores on primary producers are rarely compared across ecosystems that vary in potential primary productivity. Furthermore, proposed mechanisms to explain such patterns remain understudied. Here, I examine the strength of nutrient and grazer (herbivore) limitation (i.e., the extent to which producers’ growth is limited by insufficient nutrient supply or herbivory) of benthic algae across 13 southwest Michigan lakes that vary widely in productivity (i.e., resource supply). I compare the observed patterns of algal limitation and species composition to those predicted by two simple models: one that includes multiple species and species’ traits (the food-web model) and one that includes no variation in species or traits (the food-chain model). Species in the food-web model are assumed to display a tradeoff between resource competitive ability and resistance to herbivory (the “keystone predator” tradeoff). Among these lakes, benthic algal nutrient limitation was positive and declined significantly along a lake N:P gradient. In contrast, grazer limitation was negative and was not significantly related to any of the measured lake productivity variables. Negative grazer limitation indicated that the removal of grazers caused unexpected declines in algal biomass, which were potentially due to indirect, positive effects (e.g., nutrient recycling) of grazers. Nutrient limitation was significantly stronger than grazer limitation across lakes, which was more consistent with the food-web versus food-chain model. Changes in algal composition were also broadly consistent with predictions of the food-web model in that vulnerable, superior nutrient competitors dominated in low productivity lakes and more grazer-resistant species were observed in high productivity lakes. In general, these results point to the importance of examining limiting factors across systems and the consideration of key species’ traits when predicting and interpreting patterns.     

Benthic resources are the key to Daphnia middendorffiana survival in a high arctic pond

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a ¹³C‐enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the ¹³C‐enrichment of benthic mats with progressively increasing δ¹³C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C m^?2 day^?1) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C m^?2 day^?1), whereas benthic primary production alone (145 mg C m^?2 day^?1) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient‐limited high arctic ponds.     

The response of planktonic and microbenthic algal assemblages to nutrient enrichment in shallow coastal waters,southwest Sweden

Field and laboratory nutrient (nitrogen and phosphorus) enrichment experiments were performed using natural phytoplankton and microphytobenthic assemblages from the brackish water Öresund, S.W. Sweden. The response of algae from a low-nutrient area (Falsterbo Canal) was compared to that of algae from a polluted, nutrient-rich area (Lomma Bay).The biomass (measured as chlorophyll a) of both phytoplankton and microphytobenthos from the Falsterbo Canal increased after the addition of nitrogen. Phytoplankton growth was stimulated by the addition of phosphorus to the nitrogen-rich water of the polluted Lomma Bay. Sediment chlorophyll a showed no significant increase after the addition of nutrients in the Lomma Bay. In containers without sediment, phytoplankton uptake was calculated to account for ≈ 90% of the disappearance of inorganic fixed nitrogen from the water. In the sediment containers the microphytobenthos was estimated to account for ≈20% of the nitrogen uptake. The rest was presumably lost mainly through denitrification.When containers with microphytobenthos from Lomma Bay were kept in the dark, phosphorus was released at a rate of up to ≈ 180 μM · m^?2 · day^?1. We suggest that by producing oxygen microbenthic algae keep the sediment surface oxygenated thereby decreasing phosphorus transport from the sediment to the overlying water.     

北京河流底栖硅藻沿城乡梯度带空间分布及其季节变化

研究了北京市区沿城乡梯度带河流底栖硅藻的空间分布及其季节变化特征。通过在2014年的春季、夏季和秋季在山区对照溪流、城市上游河道和城市下游河道3个样区,共23个样点进行了底栖硅藻样品采集。分析表明,主要优势种的空间差异明显。在对照溪流,主要优势种为极小曲丝藻(Achnanthidium minutissimum);在城市上游河道,主要优势种分别为短文假十字脆杆藻(Pseudostaurosira brevistriata)和连结十字脆杆藻腹面变种(Staurosira construens var.venter);在城市下游河道,主要优势种为谷皮菱形藻(Nitzschia palea)。然而,3个样区内的主要优势种相对丰度季节变化较小(P0.05)。其中,A.minutissimum及P.brevistriata的季节变化特征均为春季秋季夏季,而S.construens var.venter及N.palea的季节变化特征均为春季夏季秋季。结果发现,北京市城乡梯度带的河流硅藻种类组成差异较大,但主要优势属种季节变化相对较小,表明硅藻种类能较好地反映城乡梯度带的河流环境变化状况,可用于北京市河流水质生物监测。     

Comparison of the Benthic Size Structure Between Sublittoral,Upper-slope and Deep-Sea Areas of the Western Pacific

Benthic size structures were compared between sublittoral, upper-slope and deep-sea areas of the Western Pacific using the mesh-size fractionated distribution of organisms. The average size of the individuals became smaller with increasing water depth, suggesting that the dwarfism is a more common phenomenon than the gigantism in the deep sea. Nonetheless, the mesh size of 0.037 mm was fine enough to retain meiobenthic specimens quantitatively. When the whole benthos was divided into macro- and meiofauna, the size distributions overlapped considerably in a mesh-size fraction between 1.0 and 0.5 mm. In this fraction, the meiofauna predominated over macrofauna in the deep sea, while the opposite applied to the shallower depths. From these results, recommended mesh sizes of the sieves for the studies of macro- and meiobenthos were proposed.     

Benthic invertebrate recolonization of small-scale disturbances in the littoral zone of a subtropical Florida lake

Construction of spawning beds by the exotic cichlid fish, Sarotherodon aurea, produces numerous small-scale disturbances in shallow Florida lakes. Two experimental methods were used to simulate these disturbances (containers filled with defaunated sediment and disturbed natural substratum) and to determine benthic invertebrate recolonization patterns and rates.Recolonization of experimental containers was rapid and densities of macroinvertebrates reached equilibrium with the control habitat by Day 6 following disturbance. However, Chironomidae and miscellaneous taxa usually were more abundant (p < 0.05) in the experimental containers, and Oligochaeta always were more abundant (p < 0.01) in the control. Species of the planktonically dispersed insects either attained equilibrium rapidly or showed significantly higher densities in the experimental containers (i.e. opportunistic species).In the second experimental approach, disturbance of natural substratum removed 91% of the benthic invertebrates. The common species of chironomids reached equilibrium by Day 6 but the two predominant oligochaetes, Limnodrilus and Pristina, reached equilibrium at 9 and 15 days respectively. For the entire community, similarity on Day 6 was 87.1% and over the remainder of the sample period averaged 86.8%. Chironomid instar analyses showed significantly higher proportions of early instars in the disturbed patch indicating that colonization is principally by younger organisms. Thus, small-scale disturbance in freshwater benthic communities may be more important in ordering the biomass or age-group structure than the numerical abundance.     

Mineralization of N and P along a trophic gradient in a freshwater mire

Release of inorganic nitrogen and phosphorus in the soil of a peatland (fen) in The Netherlands was measured by means of an in situ incubation technique. Three sampling stations were chosen along a gradient in the plant productivity and water chemistry of the fen. The station with the highest biomass production was located near the ditch that supplied the fen with water in amounts matching water losses through evaporation and downward percolation to the groundwater. Water chemistry at this station strongly resembled that of the ditch water. The two stations remote from the ditch had much lower plant biomass, and significantly lower pH, conductivity, and calcium and bicarbonate concentrations. The vegetation at these two stations was characterized by a thick Sphagnum carpet.The release of inorganic N and P was much faster at the two stations remote from the ditch than at that located near the ditch. The differences in mineralization rate are probably due to the differences in water chemistry; phosphates are more soluble at low than at high pH. The fast N mineralization at stations with a thick Sphagnum carpet may be related to the chemical composition of Sphagnum litter. The difference in productivity is not explained by the N and P mineralization rates. Direct supply of N and P from the ditch are probably the main cause of the high productivity at the station bordering the ditch.     

Changes in periphytic algal community structure as a consequence of short herbicide exposures

Effects of the triazine herbicides simazine and terbutryn on total biovolume and community structure of haptobenthic periphytic algal communities within in situ marsh enclosures are described. Levels of biovolume inhibition in excess of 98% relative to an untreated control were observed at all levels of terbutryn tested (0.01, 0.1 and 1.0 mg l^–1). No reduction in total biovolume was observed at 0.1 mg l^–1 simazine, with increasing inhibition (to 98%) at 1.0 and 5.0 mg l^–1. Following incidental enclosure flooding and removal of herbicide, increases in biovolume were observed in all but the highest treatment levels, with rates of colonization similar to that of the control.Pre-flood community structure of periphyton in simazine-treated enclosures was qualitatively similar to that of the control, while a small blue-green alga was abundant only in terbutryn-treated enclosures. After flooding, substratum colonization in most experimental enclosures was dominated by the diatom Cocconeis placentula, while this taxon accounted for about 25% of total biovolume on substrata from the control and 0.1 mg l^–1 simazine enclosures. It is concluded that periphyton successional processes, which normally lead to the development of a complex 3-dimensional mat, may be averted by short herbicide exposures.     

Plant community response to nitrogen and phosphorus enrichment varies across an alpine tundra moisture gradient

Background: The extent to which nutrient availability influences plant community composition and dynamics has been a focus of ecological enquiry for decades.

Aims: Results from a long-term nitrogen (N) and phosphorus (P) addition experiment in alpine tundra were used to evaluate the importance of the two nutrients in structuring plant communities in three communities that differed in their snow cover amounts and duration and soil moisture characteristics.

Methods: A factorial N and P experiment was established in three meadows differing in initial vegetation composition and soil moisture. Plant and soil characteristics were measured after 20 years, and the dissimilarity among meadows and treatments were measured using permutational analysis of variance.

Results: Plant species richness declined uniformly across the three meadow types and in response to N and N + P additions, while both evenness and the Shannon diversity index finding indicated that nutrient additions had the highest impact on moister habitats. Overall, N impacts overshadowed changes attributed to P additions, and the N and N + P plots in wet meadow sites were the least diverse and scored the lowest dissimilarity averages among treatments. Dissimilarity estimates indicated that the control and P plots in the dry meadow community were more distinct in composition than all other plots, and especially those in the moist or wet meadows. Above-ground biomass of grasses and sedges (graminoids) increased with N additions while forbs appeared to show responses dictated in part by the graminoid responses. The most abundant grass species of moist and wet meadow, Deschampsia cespitosa, dominated N and N + P plots of the wet sites, but did not show a N response in moist areas in spite of its general abundance in moist meadow. Competition from other plant species in the moist areas likely diminished the D. cespitosa response and contributed to the resilience of the community to nutrient enrichment.

Conclusions: Initial community composition, as influenced by the specific moisture regime, appears to control the extent to which changes in nutrient resources can alter plant community structure. Long-term fertilization tends to support most but not all findings obtained from shorter-termed efforts, and wet meadows exhibit the largest changes in plant species numbers and composition when chronically enriched with N.