Remnant Pools Research Articles

Forest ditch maintenance impoverishes the fauna of aquatic invertebrates: Opportunities for mitigation

One of the main factors causing biodiversity loss in wetlands is drainage, nevertheless, even drained areas may provide habitat for aquatic fauna in the form of drainage ditches. Assemblages in ditches are regularly disturbed by ditch maintenance, but the extent of these disturbances and mitigation possibilities are poorly documented. We conducted an experimental study in three commercially managed forest plots in eastern Estonia, aiming to find out how ditch network maintenance (DNM) affects the diversity and assemblages of aquatic macroinvertebrates in ditches and remnant pools, and whether this effect can be alleviated by constructing mitigation waterbodies. For comparison we also collected data from natural pools in three undrained forest plots. Before DNM, ditches supported greater number of higher taxa compared to remnant and natural pools and more strictly aquatic taxa, whereas natural pools in undrained plots supported more Trichoptera shredders. After DNM, the diversity in remnant pools decreased. Moreover, majority of the pools dried out, which resulted in further reduction of the richness and abundance of macroinvertebrates. In ditches the diversity dropped immediately after DNM, but recovered in two to three years. Nevertheless, plot-scale richness and abundance did not completely recover. Assemblage shift in ditches took place right after DNM and remained distinct after the four year survey period. Mitigation pools provided habitat for several taxa (especially Odonata) uncommon in other waterbodies in drained and undrained plots. Our results show that DNM in forests substantially impoverishes habitat availability and reduces the abundance and diversity of aquatic macroinvertebrates. We recommend retaining uncleaned sections in ditches and constructing mitigation pools as tools for supporting wetland biodiversity in drained forests.

Biodiversity value of remnant pools in an intermittent stream during the great California drought

Abstract In many intermittent streams, remnant pools persist after flow ceases and provide refuge for aquatic organisms able to tolerate stagnant water conditions. The conservation value of these pools may be greatly under‐appreciated, especially in regions with a Mediterranean climate, where perennial streams have been substantially modified or disturbed by human activities. Fish, amphibians, aquatic reptiles, and aquatic invertebrates were sampled from 15 remnant pools and three seeps at Coyote Creek, California, USA, in the late summer of 2014, during the height of the most intense drought that California has experienced in 500 years. Patterns of vertebrate and invertebrate species richness and community composition were compared with abiotic factors (e.g. water quality and habitat size). Thirteen vertebrate species and 172 invertebrate taxa were identified from remnant pools and seeps. Overall vertebrate richness and composition were not correlated with abiotic factors, but fish species richness increased with remnant pool size and depth. Invertebrate taxon richness increased with pool size. Invertebrate community composition differed by habitat type (pool versus seep) and gradients in composition were correlated with several abiotic factors (e.g. pool size, substrate, and canopy cover). Remnant pools at Coyote Creek supported a full assemblage of native fishes and numerous imperilled taxa, including California red‐legged frogs and California floater mussels. Nearly all native fishes and imperilled taxa are absent from artificially perennial and urbanized reaches of Coyote Creek just a few kilometres downstream of the study area. Remnant pools in intermittent streams should be a focus of conservation efforts in regions with a Mediterranean climate, especially during extreme droughts. Native fauna adapted to harsh intermittent flow regimes can thrive in these habitats, whereas non‐native taxa may fare poorly. Furthermore, remnant pools supported by deep groundwater sources, such as those along geological faults, may provide both ecological refuge and evolutionary refugia for freshwater biota.

Functional Assemblages of Macroinvertebrates in Pools and Ditches in Drained Forest Landscape

Artificially drained commercial forests are hydrologically novel ecosystems, where the array of aquatic habitats consists of ditches and remnant pools. In general the network of ditches has been found to have longer hydroperiod, the knowledge, however, about aquatic invertebrates in this system is scarce. We examined which environmental factors are impacting the biomass and abundance of functional feeding groups. Scrapers and shredders were aggregated to ditches and gatherers to pools. Filterers’ distribution pattern suggested that the function of filtering is carried out by different taxa in pools and ditches. Ditches were rather more suitable for feeding groups that rely on autochthonous resources. Acidity was a major driver of functional community composition, for example, one of the causes for higher scraper frequency in ditches. Predators exhibited greater quantities in extensive macrophyte cover regardless of water body type. Our results suggest that the trophic organization in ditches and pools is different because habitat factors select the feeding groups directly through food resources, but also because of the environmental filter on the other biological traits of the organisms. To support complex ecosystems with several trophic levels also in commercial forests, we suggest to avoid destroying macrophyte rich pools and ditches during silvicultural management.

Patterns, drivers and implications of dissolved oxygen dynamics in tropical mangrove forests

Estuarine mangrove forests regulate and facilitate many ecological processes, and provide nursery ground for many commercially important species. However, mangroves grow in sediments with high carbon loading and high respiration rates which can potentially influencing the dissolved oxygen (DO) dynamics of tidal water flowing into mangrove forests, as bacteria strip DO from the incoming water to carry out metabolic functions. In turn this is likely to influence the way nekton and other aquatic organisms utilize mangrove forests. Despite these possibilities, previous work has focused on looking at DO dynamics within mangrove creeks, with little research focusing on understanding DO dynamics within the mangrove forests themselves during tidal inundation or of DO levels of pools within the forest remaining once the tide has ebbed. The present study investigates the pattern in DO at various distances within an estuarine Rhizophora stylosa forest in tropical north Queensland. DO levels were recorded at 5 min interval over 2 days and multiple tidal cycles, data were collected between 2013 and 2014 for a total of 32 tidal cycles encompassing multiples seasons and tidal amplitudes. There were substantial fluctuations in DO, often varying from normoxic to hypoxic within the same tidal cycle. A range of factors influenced DO dynamics, in particular: tidal height, amount of sunlight, tidal phase, and distance from the outer edge of the mangrove forest. In fact, spring tides tend to have high DO saturation, particularly during the flooding phase, however as the tide starts ebbing, DO depletes rapidly especially in areas further inside the forest. Moreover during tidal disconnection the remnant pools within the forest quickly became anoxic. These variations in DO suggest that the use of mangrove forests by animals is likely to be constrained by their ability to withstand low DO levels, and provides a plausible explanation for the apparent paucity of benthic organism observed inside similar mangrove forest in previous studies of South Pacific mangroves. Low DO levels coupled with low densities of benthic prey also provides a likely explanation for the limited utilisation of landwards areas of these forests by fish and other nekton.

Aquatic invertebrate communities exhibit both resistance and resilience to seasonal drying in an intermittent coastal stream

Species inhabiting intermittent streams must survive flow cessation and drying in situ (resistance) or recolonize temporary habitats when flow returns (resilience). Some studies have found that species are resistant to seasonal drying and can persist in small remnant pools after flow ceases, while others observed rapid declines in species richness when flow ceases. However, relatively few studies have demonstrated both resistance across dry seasons and resilience across multiple wet and dry cycles. Here, we quantify seasonal and interannual changes in aquatic invertebrate community structure from 2009 to 2012 in a coastal California intermittent stream. We predicted that temporary pools and riffles would have lower richness and distinct assemblages when compared to perennial pools, and that richness would decline across the dry season. Temporary riffles exhibited lower richness values than pools, but we found no richness differences, and small compositional differences, between perennial and temporary pools. Furthermore, invertebrate richness, density, and composition changed significantly in temporary pools only immediately before drying, when depths declined >80%. These results suggest that invertebrate communities at John West Fork were not only resilient (exhibiting recovery in <6 months) to flow cessation, but also were resistant to declining water levels across the dry season.

Macroinvertebrate community responses to duration, intensity and timing of annual dry events in intermittent forested and pasture streams

Intermittent streams comprise the majority of stream length in many parts of the world, particularly dry regions. Many dry regions are expected to experience longer and more intense dry periods as the global climate changes. The response of benthic macroinvertebrate communities in intermittent streams to current variability in dry-period duration and intensity may predict their future response to climate change, but such responses require quantification in different stream types and climate zones. I compared the macroinvertebrate community among drier and wetter years from 2008 to 2012 in intermittent forested and pasture streams in a relatively warm, dry region of New Zealand. I predicted that macroinvertebrate communities would decline in density and taxonomic richness with increasing dryness, and that drought-sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa would show a stronger response than Diptera and non-insects. EPT richness and density did decline with increasing dry period duration, whereas total macroinvertebrate density and richness, and Diptera richness, showed weak and/or non-significant relationships. I predicted that loss of remnant pools (a potential dry-season refuge) would cause a decline in macroinvertebrate richness and density, but found no significant difference between years with and without pools. I predicted that years when flow resumed late in the autumn (when temperatures are too cool for insect flight) would have lower EPT richness and density than years when flow resumed early, and results confirmed this. Intermittent pasture stream communities showed a weaker response to dry period duration than communities in intermittent forested streams, as taxa relatively tolerant of agricultural stressors are also relatively tolerant of drying. Results suggest that global climate change will cause a loss of drought-sensitive species from intermittent streams in this region.

Macroinvertebrate survival during cessation of flow and streambed drying in a lowland stream

Summary The number of perennial low‐order lowland streams likely to experience intermittent flow is predicted to increase in north‐western Europe. To understand the effects of such a change on macroinvertebrates, a field experiment was carried out in a currently perennial sandy lowland stream. Using a before–after control–impact design, the flow regime was manipulated to yield two distinct treatments: stagnation (although with little water loss) and drying of the stream (although artificial remnant pools remained in the bed). There was also an unmanipulated control reach. The two treatments were applied simultaneously in separate, consecutive reaches, resulting in 29 days of stagnation and 25 days of streambed drying with surface water only present in the remnant pools. Changes in macroinvertebrate richness, abundance and community composition were recorded, and we assessed whether these changes could be explained by ecological preferences for flow of the various taxa. Stagnation resulted in only minor changes in community composition. A small number of rheophilic taxa disappeared, while taxa preferring standing waters complemented those already present, increasing total biodiversity. In remnant pools in the otherwise dry reach, richness and abundance peaked after they became isolated, indicating a concentration of invertebrates. A subsequent steep decline in richness coincided with hypoxia and increasing conductivity. Culex pipiens/torrentium colonised the pools and was then dominant. Only a small subset of the assemblage successfully used the dry streambed as a refuge. The effect of a shift from perennial to intermittent flow evidently depends on the degree of habitat change. Environmental conditions after cessation of flow are crucial in determining lowland stream macroinvertebrate persistence during water drawdown.

The population biology of mitigation: impacts of habitat creation on an endangered plant species

Conservation practitioners widely agree that optimal conservation strategies will maximize the amount of genetic variation preserved in target taxa, but there is ongoing debate about how that variation should be distributed through restoration and mitigation activities. Here, we evaluate the impacts of ~10 years of mitigation on the population genetic structure of Limnanthes vinculans, a state- and federally-listed endangered plant species restricted to ephemeral vernal pool wetlands in the Santa Rosa Plain of California. Using microsatellite loci to estimate patterns of neutral molecular variation, we found that created pools support similar levels of variation in L. vinculans as natural pools. Habitat creation and seed translocation have not disrupted the largest-scale patterns of population structure across the species range, but a concentration of mitigation activity towards the range center has reduced the extent of isolation-by-distance operating in this region and shifted the location of at least one genetic boundary. Patterns of genetic variation among populations in remnant vernal pools reveal that gene flow has historically occurred beyond the scale of individual pools at the center of the species range, while small genetic populations have differentiated around the range margins. On average, L. vinculans in created pools exhibit less cover and more restricted local distributions than those in remnant pools, but these patterns were driven by two particularly productive natural sites rather than consistent differences between natural and created sites. We conclude that mitigation activities have changed the historical patterns of gene flow within the species range to a moderate degree, that these changes will likely impact remnant pools through gene flow, and that current created sites provide less heterogeneous habitat for L. vinculans than do natural pools. Studies that track individual plants will be needed to determine if the changes in gene flow due to mitigation will have positive or negative impacts on the demographic and microevolutionary trajectories of L. vinculans. More generally, this study provides a retrospective analysis of the outcome of managing an endangered plant species through intensive mitigation, and yields several insights to inform future conservation strategies.

Smallmouth Bass Summer Habitat Use, Movement, and Survival in Response to Low Flow in the Illinois Bayou, Arkansas

AbstractThe southwestern edge of the natural range of smallmouth bass Micropterus dolomieu contains streams that become disconnected pools during summer primarily owing to hydrogeologic conditions, including high evapotranspiration rates. These conditions may complicate fisheries management by affecting fish behavior or mortality rates. The objectives of this study were to characterize summer habitat use by smallmouth bass, estimate the changes in the extent of available habitat, describe summer movement patterns, and estimate summer survival rates. Radio transmitters were implanted into 60 smallmouth bass during May 2006, and the fish were tracked until October in the forks of the Illinois Bayou, which drains a portion of the Ozark National Forest. Habitat characteristics were measured as the summer progressed, and during this time most riffle–run habitat dried completely, resulting in a series of disconnected pools. The decreases in wetted area exceeded 55% in certain 2‐km study reaches; however, smallmouth bass were consistently found at a median depth of 0.80 m. Boulder habitat was preferred when it was available; however, cobble, gravel, and bedrock substrates were also used. By July, velocity was below detection levels and water temperature occasionally exceeded 30°C. The average distance moved by smallmouth bass was 270 m in May, decreasing to 54 m by July. The distances moved were greater on average but more variable in streams with larger losses of wetted area, as fish moved away from drying areas. The survival rate was lowest in the stream most accessible to anglers. Dryness appeared to increase mortality, as survival estimates were lower than expected from published studies of streams with continuous summer flow. The effective management of fisheries under such hydrologic conditions may require preserving continuous surface flow and the quality of remnant pools as well as implementing more restrictive harvest regulations in summer.

Mining and urban impacts on semi-arid freshwater aquatic systems: the example of Mount Isa, Queensland

This paper examines the environmental risk and impact of trace metals affecting river water and sediment in and around Mount Isa, Queensland, Australia. Bacterial indicator densities are also analysed throughout the catchment to assess the impacts and the potential hazards arising from agricultural activities, sewage treatment plant releases and urban runoff. The area is drained by the ephemeral Leichhardt River, which bisects Mount Isa City and the major Pb, Zn, Cu and Ag Mount Isa Mine. Runoff is captured downstream in Lake Moondarra, with the water being used following natural filtration via a lagoon-reed bed system for potable purposes by the residents of Mount Isa City. During the dry season, the channel is characterised by numerous pools that act as storage zones for sediment and water-soluble metals as well as urban and agriculturally derived nutrients and pathogens. Our results show that sediment and water quality within the Leichhardt River adjacent to and downstream of the mine frequently exceed Australian government sediment guidelines with average values of Cu, Pb and Zn found adjacent to the footprint of the mine being 1550, 510 and 470 mg kg(-1), respectively. Dry season analysis of water-soluble Cu, Pb and Zn concentrations within pools showed that Australian government low trigger guidelines are exceeded in 100, 46 and 100% cases, respectively. The densities of bacterial indicators in remnant pools throughout the Leichhardt River also exceeded acceptable guidelines. Maximum dry season faecal coliform densities of 2000 colony forming units (CFU) per 100 mL and Enterococcus counts of 900 organisms per 100 mL were recorded in dry season remnant pools compared to wet season maximum faecal coliform and Enterococcus densities of 119 000 CFU per 100 mL and 95 000 organisms per 100 mL, respectively. The impacts on biota were also examined by assessing the metal content of the tissue of seven fish from Lake Moondarra for their Cd, Cu, Hg, Pb and Zn concentrations. Tissue metal values were generally low with only a few samples having Cu and Zn values in excess of the recommended Australian retail guideline values for fish suitable for human consumption. The effectiveness of the City's natural reed bed potable water processing facility for removing metals held within the water body (soluble and particulate) was also assessed. The results show that the treated water generally meets Australian drinking water guidelines. Overall it is clear that sediment and water quality in the area upstream of the potable water storage zone is seriously impaired. The combined effects of industrial, agricultural and urban activities present a considerable risk to the consistency and reliability of water quality, especially during highly turbid wet season flows, which transfer highly elevated concentrations of water-soluble metal and microbial contaminants.

Measurement and modelling evaporation for irrigated crops in north-west Mexico

The surface energy balance and near-surface weather variables were measured during the complete growth cycle of cotton and wheat crops planted in two successive seasons in 1995–1996 at a field site in the Yaqui Valley in Sonora, Mexico. These data were analysed in terms of a set of simple evapotranspiration models, which included the Penman–Monteith equation applied at both the hourly and daily time-scales and four semi-empirical simplifications of that equation. The field data were used to investigate and specify seasonal variations in the surface parameters (crop coefficient or surface resistance) appropriate to these models. There was a marked difference between the effective value of surface parameters for the (cotton) row crop and the (wheat) continuous-cover crop during and immediately after periods of flood irrigation. This difference reflects the fact that wet soil and remnant pools of irrigation water are well exposed to the atmosphere for flood-irrigated row crops and that evapotranspiration rates are enhanced. It proved possible to incorporate a description of this phenomenon by including a simple, additional term in an otherwise traditional model of the seasonal variation in crop factor or surface resistance. Once the parameters in the various models had been optimized against field data, all the models provided reasonable descriptions of the measured evapotranspiration. However, the Penman–Monteith equation applied at the hourly time-scale performed least well and required greater parameterization; hence, its use in this application is not justified. At the daily time-scale, use of the Penman–Monteith equation or Shuttleworth's reference crop evaporation (with a crop factor) is arguably preferable to the others in that, having more realism, it provides a description in which the (calibrated) surface parameters are a purer measure of crop control. However, in terms of descriptive ability after local calibration, the Penman, Priestley–Taylor, and Makkink models proved superior in this study. The good performance of the Makkink formulation is particularly encouraging because this equation requires only incoming solar radiation, which can be readily estimated from remotely sensed data. © 1998 John Wiley & Sons, Ltd.

Ecology of leptocerid caddisfly larvae in an intermittent South Australian stream receiving Eucalyptus litter

SUMMARY. 1. Brown Hill Creck, a small intermittent stream in dry sclernphyll forest in South Australia, flows for about 6 months during winter and spring. When flow ceases the stream dries to isolated pools which receive high summer inputs of Eucalyptus obliqua litter. Decomposition of this material in remnant pools causes extremely dark waters and depressed oxygen concentrations for up to 90 days.2. Only two fully aquatic insect species, Lepntorussa darlingtoni and Lectrides varians (Trichoptera: Leptoceridae), persist under these conditions. Both utilize litter as food, but have different feeding strategies. The more abundant L. darlingtoni ingests organic and microbial material from leaf surfaces, whereas L. varians is a leaf shredder.3. Larval processing budgets based on laboratory and fleid experiments indicated that L. variant has a greater impact on litter decomposition rates than L. darlingtoni. However, because of low density, low oxygen concentrations in pools during summer, and rapid flushing of litter from pools once flow recommences. L. variaus larvae process a small proportion of the total litter input.

The use of drinking sites, wallows and salt licks by herbivores in the flooded Middle Zambezi Valley

SummaryIn the unflooded Middle Zambezi Valley, water was available for drinking in zoogenous pools in the deciduous woodlands of the escarpment hills only during, and for a short period after, the rains. For 5 or 6 months each year these pools were dry. During the dry season the majority of large mammals drank either from remnant pools in stream beds, or migrated to the Zambezi flood plain where water was available in the Zambezi River and in pools on the flood plain. In the part of the valley filled by Lake Kariba the Zambezi and its flood plain have been inundated, and the lake shore now lies permanently in the deciduous woodlands of the escarpment hills. Although the former riverine dry‐season water sources have been removed, new sources are available along the lake shore. The suitability of the shore as a drinking site is affected by its exposure to wave action, its pitch, its soil type, and the vegetation type abutting on it, as well as by the preferences of the species using it. Elephant modify drinking sites on the shore by digging water‐filled holes at the water's edge in clay soil, and elephant, buffalo and rhinoceros create wallows in similar situations. The holes dug by elephant are much used by antelope, especially impala, for drinking. By analogy with elephant‐created pools in the woodlands, these zoogenous pools on the lake shore may have been a source of sodium for species drinking there. Such sources were not widely available in the dry season in the unflooded Zambezi Valley.