Sediment biogeochemistry along an oyster aquaculture chronosequence

Oyster aquaculture is expanding globally, and there has been a recent research surge examining how oyster farms alter coastal ecosystems. Yet, until now, the role of time in these studies has largely been missing. Here we used an in situ chronosequence approach to determine how the presence of oyster aquaculture (Crassostrea virginica) altered sediment nitrogen (N), oxygen (O2), and phosphorus (P) cycling. Overall we found that the sum of nitrogen fluxes increased significantly following addition of aquaculture, and switched from net N consumption (i.e. net nitrogen fixation: -14.41 µmol N m-2 h-1) to production (i.e. net denitrification: 553.57 µmol N m-2 h-1). Ammonium (NH4+) fluxes did not differ between bare sediment and oyster aquaculture. Additionally, both the magnitude of N2 and NH4+ fluxes oscillated on an annual scale of aquaculture age, but not predictably so. We observed significantly more variance (σ2) in dinitrogen and NH4+ fluxes in sediments beneath aquaculture, indicating increased non-linearity. O2 fluxes increased from Years 4 to 6, before returning to baseline conditions. There were no differences in sediment P cycling. This study demonstrates that sediment biogeochemical processes can become non-linear under the pressure of oyster aquaculture, and this non-linearity likely has important implications for ecosystem function.

Perubahan Struktur Vegetasi Pada Sistem Perladangan Gilir Balik Masyarakat Dayak Pitap Kalimantan Selatan

Shifting cultivation is cultivation system performed alternately from one field to another on forest lands. This study aims to assess changes in structure and composition of vegetation and determine the conditions of environmental factors during shifting period. This research use chronosequence approach at sites with different ages i.e. two, four, six and eight years compared to natural forest using structured form squares (20x100 m2) belt transect comprising several terraced plots. Vegetation parameters were measured for all forms, environmental factors measured were microclimates and edafic factors and soil macro-nutrient content. The results showed that 42 species of 23 families founded in all forms. The vegetation distribution from diameter classes (KD) indicated that KD 0-10 cm had the highest number of individual density from all research site and declined sharply with the increase of KD. The potential regeneration of tree species vegetation component of each site showed some different patterns. In aspect of microclimates, the temperature decreases along with sites age. Edafic factor did not show any clear pattern with increase of sites age for C, N and P, while soil K levels were significantly higher in the youngest site age than the older sites.

Reclamation is not the primary determinant of soil recovery from oil and gas development in Wyoming sagebrush systems

Dryland soils store approximately 10-15% of the world’s soil organic matter (SOM) to 1 m. Threats to carbon stocks in global dryland soils include cultivation, overgrazing, urbanization, and energy development. To limit loss of carbon from these soils, it is important to understand, first, how disturbances affect SOM and second, how SOM recovers after disturbance. In this study, we address current gaps in our understanding of the effects of oil and gas development and reclamation on SOM in the sagebrush steppe of Wyoming, a cold temperate shrub-dominated dryland. Most studies have found that soil disturbance, including from the respreading of topsoil during wellpad reclamation, is damaging to SOM stores; however, research on ~80 year old unreclaimed oil and gas wellpads found no difference in SOM between wellpads and undisturbed sites. Using a chronosequence approach and paired study design, we evaluated the effects of reclamation on SOM by comparing undisturbed sites to wellpads where reclamation activities either had or had not occurred. Our results suggest that the most important factor in recovery of SOM after disturbance in this area was not the presence or absence of reclamation, but time since wellpad abandonment and spatial heterogeneity of plants. Further study on the effectiveness of different reclamation techniques is warranted if the goal of reclamation is to aid SOM recovery and prevent further C loss from these systems.

Plasticity and Stereotypy in Avian Foraging during Secondary Succession in Temperate Forests

Some bird species cannot persist during early secondary succession after natural or anthropogenic disturbance of Australian Mountain Ash ( Eucalyptus regnans) forest, whilst others remain abundant throughout regeneration. To conserve bird species diversity optimally in such forests, we need to know, inter alia, exactly why the latter species can persist after disturbance. Using a chronosequence approach, we documented four facets of foraging in a suite of these persistent species effectively covering 100 years of succession in E. regnans forest disturbed by wildfire or timber harvesting, namely the foraging strata, locations, substrates and behaviours used. Most species showed plasticity in their use of foraging strata and locations during succession, but four exhibited some limited stereotypy in these facets. In contrast, use of foraging substrates and behaviours was largely invariant within species during secondary succession. We suggest that switching foraging strata and locations was probably critical to persistence of most of these bird species during secondary succession, given the marked variation in structural and floristic variables that characterises this regeneration process. Some plasticity in foraging behaviour repertoire and substrate use was probably possible, but not beneficial. Although some resident bird species’ populations were severely reduced by disturbance in these forests, a substantial subset of species was sufficiently flexible in choosing foraging microhabitats to persist throughout secondary succession at pre-disturbance abundances.