Land-use Gradient Research Articles

Drivers for ammonia-oxidation along a land-use gradient in grassland soils

In this study, drivers for ammonia-oxidation and the related microbial communities (ammonia-oxidizing bacteria and archaea) were investigated in grassland soils on the local as well as on the regional scale focusing on the role of land-use intensity (LUI). To this end, 150 sites from three distinct regions across Germany were selected, covering the whole range of LUI levels (from natural grasslands up to intensive managed meadows). Furthermore, the role of contrasting soil types was analyzed in one of the regions (high vs low organic matter content) for ammonia-oxidation. We revealed a significant increase in potential nitrification rates and abundance of ammonia-oxidizing microbes at two sites on the local level from extensively to intensively managed sites, which indicates that the response pattern of ammonia-oxidizing microbes in grassland soils is likely triggered to a large extent by LUI. However at a third site, where two different soil types were investigated, no correlation between LUI and potential nitrification rates was observed, and only a site-specific effect was apparent. At this site, on the one hand the specific soil type (Histosol) and the related continuous nutrient mobilization from the former peat matrix, as well as the high groundwater level, which could induce a high abundance of methane- oxidizing microbes in the top soil, may be of greater importance as a driver for potential nitrification rates and abundance of ammonia- oxidizing microbes than LUI. On the other hand, the mineral soils of this site were characterized by extreme water shortage, which may also explain the lack of potential nitrification and the abundance of ammonia-oxidizing bacteria and archaea. Thus any extrapolation of local data to regional predictions must be made with care, as factors other than LUI may be of importance if the nitrification potential of a soil is to be described.

Tree Growth and Resilience to Extreme Drought Across an Urban Land-use Gradient

Understanding the response of urban forests to extreme climatic events, such as drought, will be essential to predicting impacts of climate change on the urban tree canopy and related ecosystem services. This study evaluated variation in tree growth and drought resistance (growth during drought) and resilience (growth in period following drought) across four land-use categories (built, transportation, park, and semi-natural forest) and four species (Acer saccharum, Gymnocladus dioicus, Liriodendron tulipifera, and Pinus strobus) at The Morton Arboretum in suburban Lisle, Illinois, U.S. Tree growth and resistance to drought both varied as an interaction between landuse and species (F15, 100 = 5.25, p < 0.001; F15, 100 = 2.42, p = 0.005). Resilience of tree growth to extreme drought was generally high and did not vary across species and land-uses. In this study, individual tree species responses to drought varied across land-uses, illustrating the difficulty of predicting the reaction of urban forests to projected increases in the frequency of extreme climatic events. Tree growth response to drought varied even across the relatively narrow range of growing conditions studied here. Investigation of a broader range of sites, encompassing the full urban forest continuum, would likely demonstrate even greater variation in tree response to extreme climatic events.

Land-use change, not climate, controls organic carbon burial in lakes

Lakes are a central component of the carbon cycle, both mineralizing terrestrially derived organic matter and storing substantial amounts of organic carbon (OC) in their sediments. However, the rates and controls on OC burial by lakes remain uncertain, as do the possible effects of future global change processes. To address these issues, we derived OC burial rates in (210)Pb-dated sediment cores from 116 small Minnesota lakes that cover major climate and land-use gradients. Rates for individual lakes presently range from 7 to 127 g C m(-2) yr(-1) and have increased by up to a factor of 8 since Euro-American settlement (mean increase: 2.8×). Mean pre-disturbance OC burial rates were similar (14-22 g C m(-2) yr(-1)) across all land-cover categories (prairie, mixed deciduous and boreal forest), indicating minimal effect of the regional temperature gradient (approx. 4 °C) on background carbon burial. The relationship between modern OC burial rates and temperature was also not significant after removal of the effect of total phosphorus. Contemporary burial rates were strongly correlated with lake-water nutrients and the extent of agricultural land cover in the catchment. Increased OC burial, documented even in relatively undisturbed boreal lake ecosystems, indicates a possible role for atmospheric nitrogen deposition. Our results suggest that globally, future land-cover change, intensification of agriculture and associated nutrient loading together with atmospheric N-deposition will enhance OC sequestration by lakes.

Intestinal parasites of the gopher tortoise (Gopherus polyphemus) from eight populations in Georgia

The gopher tortoise (Gopherus polyphemus), one of five tortoise species endemic in the USA, was recently classified as a candidate for federal listing as a threatened species. Fecal samples collected from 117 tortoises from eight sites in Georgia were examined for endoparasites using a combination of sedimentation and flotation. Samples from an island population were examined for parasitic oocysts and ova only by flotation, protozoan cysts by trichrome-stained direct smear, and Cryptosporidium by direct immunofluorescence assay and ProSpecT rapid assay. A total of 99 tortoises (85, range 0-100%) was infected with pinworms (Alaeuris spp.), 47 (40, 0-86%) with cestodes (Oochorstica sp.), 34 (41, 0-74%) with Chapiniella spp., 2 (3, 0-33%) with Eimeria paynei, and a single tortoise each with a capillarid and ascarid (1%). On the island, Entamoeba was detected in one tortoise (2%) while Cryptosporidium oocysts were detected in eight (17%). In conclusion, at least eight species of parasites were detected including Cryptosporidium, a possible pathogen of tortoises. Interestingly, we detected spatial variation in the distribution of several parasites among populations suggesting additional work should be conducted across a gradient of tortoise densities, land use, and habitat characteristics.

Effect of Native Vegetation Loss on Stream Ecosystem Processes: Dissolved Organic Matter Composition and Export in Agricultural Landscapes

Stream and river ecosystems are dependent on energetic inputs from their watersheds and thus shifts in land use from forest cover to agriculture will affect stream community composition and function. The disruption of forest-aquatic linkages alters the organic matter resources in agricultural streams. Dissolved organic matter (DOM) is the dominant form of organic matter in aquatic ecosystems, and a microbial energy source that is important for stream respiration. The concentrations and characteristics of DOM are regulated by both terrestrial (for example, terrestrial organic matter supply) and in-stream processes (for example, microbial respiration and periphyton production) that are influenced by land management. The effects of watershed land use and topographic, soil and climatic variables on DOM quantity (dissolved organic carbon concentration and load), source (terrestrial or in-stream) and quality (composition and lability) were measured in 14 streams across an agricultural land-use gradient. DOC concentration was positively correlated with watershed pasture cover and negatively correlated with watershed relief. No watershed variables were important correlates of DOC load. Stream DOM was primarily of terrestrial origin, but DOM in agricultural streams had a greater proportion of sources from in-stream sources. This may be due to reduced connection with riparian vegetation and increased in-stream primary production. We suggest that maintaining watershed tree cover greater than 52% and ensuring less than 10% of the length of riparian corridor is cleared for pasture could minimize changes to DOM composition. This is important to avoid flow-on effects for stream ecosystem processes that are mediated by DOM. Long-term DOM monitoring will be valuable for assessing the functional impacts of land-use change.

Response diversity to land use occurs but does not consistently stabilise ecosystem services provided by native pollinators

More diverse biological communities may provide ecosystem services that are less variable over space or time. However, the mechanisms underlying this relationship are rarely investigated empirically in real-world ecosystems. Here, we investigate how a potentially important stabilising mechanism, response diversity, the differential response to environmental change among species, stabilises pollination services against land-use change. We measured crop pollination services provided by native bees across land-use gradients in three crop systems. We found that bee species responded differentially to increasing agricultural land cover in all three systems, demonstrating that response diversity occurs. Similarly, we found response diversity in pollination services in two of the systems. However, there was no evidence that response diversity, in general, stabilised ecosystem services. Our results suggest that either response diversity is not the primary stabilising mechanism in our system, or that new measures of response diversity are needed that better capture the stabilising effects it provides.

Knowledge and prevention of tick-borne diseases vary across an urban-to-rural human land-use gradient

We sought to determine the behavioral risk of exposure to tick-borne diseases across a human land-use gradient in a region endemic for diseases transmitted by the lone star tick. We measured the knowledge, attitudes, and preventive behaviors of visitors to 14 suburban, exurban, and rural recreational parks. A structured interview was conducted to determine respondents’ (n=238) knowledge of tick-borne disease risk, perceived susceptibility to tick-borne disease, and tick bite prevention behaviors. We found significant differences across park types for most personal protective behaviors. Individuals in exurban parks were more likely to perform frequent tick checks and use chemical insect repellents compared to other park types (p<0.001), while suburban park visitors were more likely to avoid tick habitats (p<0.05). Disparities exist in the level of knowledge, perceived personal risk, and use of preventive measures across the human land-use gradient, suggesting that targeted public health intervention programs could reduce behavioral exposure risk by addressing specific gaps in knowledge and prevention.

The diversity of soil mites (Acari: Mesostigmata) in yellow ant (Lasius flavus) nests along a gradient of land use

Mesostigmatid mites communities in yellow ant (Lasius flavus) hills and phoresis of mites on this ant species were analysed in the Wielkopolska Region, Central Poland. Samples were collected from ant nests located along a gradient of four different types of land use: forest, ecotone, meadow and garden. In total, 132 mites were collected in ant nests among which 26 species were identified. The highest total abundance of mites was observed in the ecotone. Moreover, 14 mite specimens were found on L. flavus workers bodies. These are the first records of phoresis of mesostigmatid mites on this ant species.

Effects of land use on soil organic carbon and microbial processes associated with soil health in southern Brazil

Carbon plays a key role in determining soil health, which is defined as the soil's capacity to maintain environmental functions and biological productivity. In this study, C cycling was evaluated in soils along a gradient of land use, from native forest (NF), reforested sites (secondary forest – SF, Araucaria angustifolia – AR, Pinus elliottii – PI), clear-cut P. elliottii stands (CT) to farmland (AG). NF, AR, and SF sites had lower litter C:N ratios than PI, CT, and AG sites. Soils under forests had more organic C than CT and AG soils, whereas soils with native species had more microbial biomass C than PI, CT and AG soils. Both metabolic quotient (qCO2) and dehydrogenase activity increased with land use. Multivariate analysis revealed that soils of AR and SF were similar to NF and differed from CT and AG, which had higher qCO2 and dehydrogenase activity, suggesting microbial stress. Litter C:N ratios and soil microbial biomass C, moisture, CO2 evolution, and cellulase activity discriminated most effectively between land uses. Reforestation with native species restored soil properties to levels similar to those in NF, being more sustainable, whereas reforestation with the exotic P. elliottii made soils more similar to AG soils.

Microbial Community Changes Along a Land-Use Gradient of Desert Soil Origin

Soil harbors remarkably stabilize bacterial communities at the phylum level. However, no two soils have exactly the same structure of bacterial phyla. The structure of microbial community is strongly influenced by the type of land-use through changes in soil attributes. Using high-throughput pyrosequencing and quantitative polymerase chain reaction techniques, soil microbial community structures were investigated along a land-use gradient of 100- and 27-year farmlands, a 33-year Pinus forest, a 28-year poplar forest, and a 21-year shrubland, as well as a native desert from which all cultivated systems were converted. The results revealed that the dominant phylotypes in the native soil comprised primarily of Alphaproteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes, accounting for > 71.4% of the total bacterial 16S rRNA sequence reads. Changes in land-use led to a significant decrease in these dominant phylotypes down to 33.4%. In contrast, the phylotypes with low abundance, such as Acidobacteria, Chloroflexi, Nitrospira, and Gammaproteobacteria, increased sharply from 4.5%5.9% in the native soil to 20.9%30.2% of the total 16S rRNA gene sequences in the cultivated soils except for the soil from the shrubland. These contrasting changes in the major taxa appear to be correlated with the changes in soil attributes. For instance, bacterial and archaeal amoA genes were found to be 960- and 3 800-fold more abundant in the soil from the 100-year farmland than the native soil. The changes in numerically less dominant nitrifying phylotypes are consistent with soil inorganic nitrogen dynamics. Quantification of the 16S rRNA genes demonstrated that bacteria and archaea were about two to three orders of magnitude more abundant in the cultivated soil than in the native soil. Hence, land-use type affects the soil bacterial community structure, which has profound consequences on ecosystem function.

Impact of habitat structure and fruit abundance on avian seed dispersal and fruit predation

So far, it is poorly understood how differential responses of avian seed dispersers and fruit predators to changes in habitat structure and fruit abundance along land-use gradients may translate into consequences for the seed dispersal of associated plants. We selected a gradient of habitat modification (forest, semi-natural, and rural habitat) characterized by decreasing tree cover and a high variation in local fruit availability. Along this gradient we quantified fruit removal by avian seed dispersers and fruit predators from 18 Sorbus aucuparia trees. We analyzed the relative importance of tree cover and fruit abundance in explaining species richness, abundance and fruit removal rates of both guilds from S. aucuparia trees. Species richness and abundance of seed dispersers decreased with decreasing tree cover, whereas fruit removal by seed dispersers decreased with decreasing fruit abundance independent of tree cover. Both variables had no effect on species richness, abundance and fruit removal by fruit predators. Consequently, seed dispersers dominated relative fruit removal in fruit-rich sites but the dispersal/predation ratio shifted in favor of predation in fruit-poor habitat patches. Our study demonstrates that variation in local habitat structure and fruit abundance can cause guild-specific responses. Such responses may result in a shift in fruit removal regimes and might affect the dispersal ability of dependent fruiting plants. Future studies should aim at possible consequences for plant recruitment and guild-specific responses of frugivores to disturbance gradients on the level of entire plant–frugivore associations.

Effects of land use on the fungal spore richness in small crater-lake basins of western Uganda

Mycological tools to estimate the effects of diverse land-use practices on fungal diversity are scarce, because of poor knowledge of the taxonomic diversity of tropical fungi and their response to anthropogenic habitat change. Here, we investigate assemblages of fungal spores, recently deposited in the bottom sediments of 24 small crater lakes in western Uganda, to assess the relationship between the local richness of fungi and environmental variation in the crater basin along regional gradients of natural vegetation and land use. We recovered ~9500 fungal spore specimens, which could be attributed to 216 morphotypes. Using an information-theoretic approach based on the corrected Akaike Information Criterion (AICc), we determined the environmental factors which best explained variation in the diversity of fungal spores among three datasets: (i) the full set of 24 crater basins, (ii) the subset of 22 basins with freshwater lakes, and (iii) the subset of 17 basins partly or completely in agricultural use (cropland, fallow land, pasture and plantation). In these 17 human-impacted crater basins our results revealed a negative relationship between fungal spore richness and the areal fraction of basins in agricultural use. However, this detrimental effect of land use on fungal spore richness was not apparent across the full set of both disturbed and (presently) undisturbed basins. This was due to large variation in fungal spore richness among the undisturbed basins covered either with forest or savannah vegetation, probably resulting from site-specific controls on fungal habitat diversity, such as climatic moisture balance and the composition of natural and/or secondary vegetation. The land-use effects on fungal spore diversity, as documented in this study, suggest that communities of tropical fungi progressively exposed to land-use practices are threatened by species loss. Hence, our study demonstrates the need to develop conservation strategies mitigating the impacts of agriculture on the biodiversity of tropical fungi.

Demography of greater prairie‐chickens: Regional variation in vital rates, sensitivity values, and population dynamics

AbstractIntensification of rangeland management has coincided with population declines among obligate grassland species in the largest remaining tallgrass prairie in North America, although causes of declines remain unknown. We modeled population dynamics and conducted sensitivity analyses from demographic data collected for an obligate grassland bird that is an indicator species for tallgrass prairie, the greater prairie‐chicken (Tympanuchus cupido), during a 4‐year study in east‐central Kansas, USA. We examined components of reproductive effort and success, juvenile survival, and annual adult female survival for 3 populations of prairie‐chickens across an ecological gradient of human landscape alteration and land use. We observed regional differences in reproductive performance, survivorship, and population dynamics. All 3 populations of prairie‐chickens were projected to decline steeply given observed vital rates, but rates of decline differed across a gradient of landscape alteration, with the greatest declines in fragmented landscapes. Elasticity values, variance‐scaled sensitivities, and contribution values from a random‐effects life‐table response experiment all showed that the finite rate of population change was more sensitive to changes in adult survival than other demographic parameters in our declining populations. The rate of population change was also sensitive to nest survival at the most fragmented and least intensively grazed study site; suggesting that patterns of landscape fragmentation and land use may be affecting the relative influences of underlying vital rates on rates of population growth. Our model results indicate that 1) populations of prairie‐chickens in eastern Kansas are unlikely to be viable without gains from immigration, 2) rates of population decline vary among areas under different land management practices, 3) human land‐use patterns may affect the relative influences of vital rates on population trajectories, and 4) anthropogenic effects on population demography may influence the regional life‐history strategies of a short‐lived game bird. © 2012 The Wildlife Society.

Free and protected soil organic carbon dynamics respond differently to abandonment of mountain grassland

Abstract. Land-use change (LUC) and management are among the major driving forces of soil carbon (C) storage. Abandonment of mountain grassland promotes accumulation of aboveground biomass and litter, but related responses of soil organic matter (SOM) dynamics are uncertain. To determine SOM-C turnover we sampled 0–10 cm of soils in the European Alps along two land-use gradients (hay meadows, grazed pastures and abandoned grasslands) of different management intensity. A first land-use gradient was located at Stubai Valley (MAT: 3 °C, MAP: 1097 mm) in Austria and a second at Matsch Valley (MAT: 6.6 °C, MAP: 527 mm) in Italy. We estimated C input and decomposition rates of water-floatable and free particulate organic matter (wPOM, fPOM &lt;1.6 g cm−3) and aggregate-occluded particulate and mineral-associated organic matter (oPOM &lt;1.6 g cm−3, mOM &gt;1.6 g cm−3) using bomb radiocarbon. In mountain grasslands average C turnover increased from roots (3 yr) &lt; wPOM (5 yr) &lt; fPOM (80 yr) &lt; oPOM (108 yr) &lt; mOM (192 yr). Among SOM fractions the turnover of fPOM-C varied most in relation to management. Along both land-use gradients C input pathways shifted from root-derived towards litter-derived C. The C input rates of both wPOM-C and fPOM-C were affected by land management at both sites. In contrast, oPOM-C and mOM-C dynamics remained relatively stable in response to grassland abandonment. Carbon accumulation rates of free POM decreased strongly with time since LUC (10, 25 and 36 yr). For wPOM-C, for example, it decreased from 7.4 &gt; 2.2&gt; 0.8 g C m−2 yr−1. At both sites, most C was sequestered in the first years after LUC and free POM reached new steady state within 20–40 yr. We conclude that w-and fPOM-C vs. oPOM-C dynamics respond differently to grassland management change and thus POM does not represent a homogeneous SOM fraction. Sequestered C is stored in the labile POM and not stabilized in the long-term. Thus, it is unlikely that abandonment, the dominant form of LUC in the European Alps, provides a substantial net soil C sink.

Resilience and stability in bird guilds across tropical countryside

The consequences of biodiversity decline in intensified agricultural landscapes hinge on surviving biotic assemblages. Maintaining crucial ecosystem processes and services requires resilience to natural and anthropogenic disturbances. However, the resilience and stability of surviving biological communities remain poorly quantified. From a 10-y dataset comprising 2,880 bird censuses across a land-use gradient, we present three key findings concerning the resilience and stability of Costa Rican bird communities. First, seed dispersing, insect eating, and pollinating guilds were more resilient to low-intensity land use than high-intensity land use. Compared with forest assemblages, bird abundance, species richness, and diversity were all ~15% lower in low-intensity land use and ~50% lower in high-intensity land use. Second, patterns in species richness generally correlated with patterns in stability: guilds exhibited less variation in abundance in low-intensity land use than in high-intensity land use. Finally, interspecific differences in reaction to environmental change (response diversity) and possibly the portfolio effect, but not negative covariance of species abundances, conferred resilience and stability. These findings point to the changes needed in agricultural production practices in the tropics to better sustain bird communities and, possibly, the functional and service roles that they play.

Algal bioassessment metrics for wadeable streams and rivers of Maine, USA

AbstractMany state water-quality agencies use biological assessment methods based on lotic fish and macroinvertebrate communities, but relatively few states have incorporated algal multimetric indices into monitoring programs. Algae are good indicators for monitoring water quality because they are sensitive to many environmental stressors. We evaluated benthic algal community attributes along a landuse gradient affecting wadeable streams and rivers in Maine, USA, to identify potential bioassessment metrics. We collected epilithic algal samples from 193 locations across the state. We computed weighted-average optima for common taxa for total P, total N, specific conductance, % impervious cover, and % developed watershed, which included all land use that is no longer forest or wetland. We assigned Maine stream tolerance values and categories (sensitive, intermediate, tolerant) to taxa based on their optima and responses to watershed disturbance. We evaluated performance of algal community metrics used in mu...

Spatial variability of soil characteristics along a landscape gradient in Bellanwila-Attidiya area, Sri Lanka

Wetlands are comprised of unique components of soil, water and biodiversity which are interconnected. This ecosystem provides important ecological, social and economic services which are often unnoticed and undervalued. Although water and biodiversity components of wetlands are being somewhat investigated, a very few research have been carried out to investigate soil properties. This study focussed on spatial variability of soil chemical and physical parameters in a land use gradient around the Bellanwila-Attidiya Sanctuary, a wetland situated in Colombo suburbs. Main objective was to present a summary of spatial variation of soil characteristics and develop maps using GIS in different land use areas: natural-wetland; manmade-functioning paddy fields, non-functioning paddy fields, residential and industrial.This study was carried out for a period of 3 months and several random soil samples were obtained from all land use areas. The following parameters were analysed in triplicate, from the samples taken at the surface and at one m depth in the soil: chemical properties; NO3- , PO43-, SO42-, Cl- and Fe3+ and physical properties; moisture content, pH, salinity, electrical conductivity, temperature, soil type and soil colour. All analysis were carried out according to Standard Methods and the GIS maps were developed using ArcView GIS 3.2. The results indicated that all chemical and physical parameters of soil varied across the landuse gradient, except for temperature. According to the GIS maps there are apparent variations in distribution of soil properties. On the surface, the highest level of each parameter was found as follows: NO3- in industrial area, PO43- in functioning paddy fields, SO42- in residential area, Cl- in residential area, Fe3+ in functioning paddy fields, moisture content in wetland, pH in industrial area, salinity in residential area, electrical conductivity in residential area. At 1 m depth, the pattern was different: NO3- in abandoned paddy fields, PO43- in functioning paddy fields, SO42- in wetland, Cl- in wetland, Fe3+ in residential area, moisture content in wetland, pH in industrial area, salinity in wetland, electrical conductivity in wetland. The findings clearly exhibit the increases in anthropogenic pressure have resulted in wide-scale alternation of soil properties, at least in the surface soil, across a land use gradient. Managing land use in the watershed of the wetland thus needs adequate attention to conserve this natural ecosystem

Lichen functional groups as ecological indicators of the effects of land-use in Mediterranean ecosystems

The effects of land-use on species and communities are usually studied by considering high-intensity land-use gradients. However, in many Mediterranean Europe areas, the traditional land-use regime is of low-intensity, including low-impact forestry practices and extensive livestock pasture. This low-intensity land-use is associated with ‘High Nature Value Farmlands’, which occupy more than 50% of total farmland area in Mediterranean areas. The objective of this work was to determine the effect of traditional low-intensity land-use on epiphytic lichen communities in Mediterranean cork-oak woodlands. We intend to investigate the value of lichen communities as early indicators of the effects of land-use changes. For that, lichens were sampled along a gradient of low-intensity land-use that included forestry and pasture activities. As lichen diversity variables we considered: (i) total species richness, (ii) total species frequency (LDV), and (iii) richness and frequency of functional groups dividing species according to their eutrophication-tolerance. We found an increase of total species richness with an increase of land-use intensity which is opposite to expectations and which was shown for first time in lichens. The increase in total species richness was due to an increase of the number of eutrophication tolerant species accompanied by the maintenance of the sensitive one when we analyzed the lichen-data at the functional response group level. These results fit with the intermediate disturbance hypothesis that predicts higher diversity under an intermediate disturbance due to the coexistence of species with contrasting ecological requirements. Traditionally managed cork-oak woodlands with low-intensity land-use can thus support a high diversity of lichen species. An important outcome was that we confirmed the importance of using ecological indicators based on functional-groups for monitoring changes in ecosystems and, since lichens responded to low levels of land-use intensity, we have also shown the possibility of using lichens as early indicators of the impacts of low intensity land-use.

Water- and sediment-quality effects on Pimephales promelas spawning vary along an agriculture-to-urban land-use gradient

Many streams in the U.S. are “impaired” due to anthropogenic influence. For watershed managers to achieve practical understanding of these impairments, a multitude of factors must be considered, including point and nonpoint-source influence on water quality. A spawning assay was developed in this study to evaluate water- and sediment-quality effects that influenced Pimephales promelas (fathead minnow) egg production over a gradient of urban and agricultural land use in 27 small watersheds in Eastern Wisconsin. Six pairs of reproducing fathead minnows were contained in separate mesh cartridges within one larger flow-through chamber. Water- and sediment quality were sampled for an array of parameters. Egg production was monitored for each pair providing an assessment of spawning success throughout the 21-day test periods. Incidences of low dissolved oxygen (DO) in many of these streams negatively impacted spawning success. Nine of 27 streams experienced DO less than 3.1 mg/L and 15 streams experienced DO less than 4.8 mg/L. Low DO was observed in urban and agricultural watersheds, but the upper threshold of minimum DO decreased with increasing urban development. An increase in specific conductance was related to a decrease in spawning success. In previous studies for streams in this region, specific conductance had a linear relation with chloride, suggesting the possibility that chloride could be a factor in egg production. Egg production was lower at sites with substantial urban development, but sites with low egg production were not limited to urban sites. Degradation of water- and sediment-quality parameters with increasing urban development is indicated for multiple parameters while patterns were not detected for others. Results from this study indicate that DO must be a high priority watershed management consideration for this region, specific conductance should be investigated further to determine the mechanism of the relation with egg production, and water- and sediment-quality degrade in relation to urban influence.

Post-Soviet agricultural change predicts future declines after recent recovery in Eurasian steppe bird populations

The socioeconomic impacts of the break-up of the Soviet Union after 1991 have resulted in massive changes in agriculture on the Eurasian (Pontian) steppe, most of which is now confined to Kazakhstan. Recent trends in agriculture are well documented but their impacts on the characteristic bird community of this vast region, which contains over 10% of the world’s remaining grasslands, are poorly understood. We modelled bird population density in a representative region in central Kazakhstan along a land-use gradient ranging from pristine steppe to arable fields and heavily grazed pastures. Long-abandoned arable fields and ungrazed pristine steppe were the most important habitats for most species, and post-1991 abandonment of arable agriculture suggests that many species have enjoyed a period of significant population growth. Livestock concentration effects, leading to high grazing pressure in small areas, are also likely to have benefitted several species of high conservation concern. However, analysis of land-use statistics and socioeconomic surveys among land managers suggest that recent and predicted future trends in agriculture in the steppe zone, particularly the reclamation of abandoned cereal fields and reduced grazing pressure, may cause populations of most species, including a number of biome-restricted species, to decline in the near future. We discuss possible conservation solutions, including improvements in the protected area system and land-sparing options.