Influence of large offshore wind farms on North German climate

Wind farms impact the local meteorology by taking up kinetic energy from the wind field and by creating a large wake. The wake influences mean flow, turbulent fluxes and vertical mixing. In the present study, the influences of large offshore wind farms on the local summer climate are investigated by employing the mesoscale numerical model METRAS with and without wind farm scenarios. For this purpose, a parametrisation for wind turbines is implemented in METRAS. Simulations are done for a domain covering the northern part of Germany with focus on the urban summer climate of Hamburg. A statistical-dynamical downscaling is applied using a skill score to determine the required number of days to simulate the climate and the influence of large wind farms situated in the German Bight, about 100 km away from Hamburg.Depending on the weather situation, the impact of large offshore wind farms varies from nearly no influence up to cloud cover changes over land. The decrease in the wind speed is most pronounced in the local areas in and around the wind farms. Inside the wind farms, the sensible heat flux is reduced. This results in cooling of the climate summer mean for a large area in the northern part of Germany. Due to smaller momentum fluxes the latent heat flux is also reduced. Therefore, the specific humidity is lower but because of the cooling, the relative humidity has no clear signal. The changes in temperature and relative humidity are more wide spread than the decrease of wind speed. Hamburg is located in the margins of the influenced region. Even if the influences are small, the urban effects of Hamburg become more relevant than in the present and the off-shore wind farms slightly intensify the summer urban heat island

Investigation on the trophic state of the North Sea for three years (1994?1996) simulated with the ecosystem model ERSEM ? the role of a sharp NAOI decline

International audienceApplying the ecosystem model ERSEM to the Northwest-European shelf (48°?63°N, 15°W?12°E) the years 1994-1996 were simulated, which exhibit an extremely strong transition in North Atlantic Oscillation index (NAOI): from a high-NAOI to a low-NAOI regime. In order to be far enough from the boundaries of the model area the results and budgets are focussed on the North Sea area. For this region the model was validated against climatological values of nitrate as representative nutrient. For all three years the North Sea was found to be net heterotrophic: organic material was imported, inorganic material was exported. The strength of this "remineralisation-machine" was large during NAOI-high years (1994 and 1995). It was weaker in 1996 with a low NAOI. This was caused by higher net primary production in the northern North Sea during summer 1996. In this year the stratification was weaker and began later allowing the deep nutrient-rich water in the northern North Sea to be mixed into the upper layers also during early summer

Research Report No. 32, Trends of Non-straight Tree Stems in Loblolly and Slash Pine Plantations in East Texas, 1985-1994

Trees from East Texas loblolly ( Pinus taeda L. ) and slash ( Pinus effiottii Engelm. ) pine plantations are one of the sources of raw material for conversion into products such as paper, veneer and lumber by East Texas forest product mills. The utilization of the planted trees may depend on various biological and economical factors. Factors such as tree size, tree condition, stumpage prices and interest rates can play a role in the merchandizing process. One of the factors, tree condition, may be affected by tree crown position in canopy, incidence of disease, single stem and straightness of stem. Trees with straighter stems may be more suitable for utilization into higher value products, such as veneer, lumber or poles rather than converted into alternative products. Stumpage prices for trees with relatively straight stems usually exceed prices offered for trees with less straight stems. An initial stand-level analysis of non-straight tree stems of planted pines in East Texas was conducted by Holley (1992). During a time period of 6 years, percentage of non-straight stems for both loblolly and slash pine trees was fairly consistent. Holley also found that tree stem straightness was not related to plantation age. The purpose of this paper is to build on the work by Holley and attempt to answer the question: do planted pines on a stand-level basis in East Texas tend to become more straight or less straight as they become older

Research Report No. 31, Observed Growth Rates of Loblolly and Slash Pine Plantations in East Texas

Of the approximately 11.2 million acres of forest in East Texas, about 2.5 million acres have been planted with loblolly pine trees ( Pinus taeda L. ) and 500,000 acres with slash pine trees ( Pinus elliottii Engelm. ). These plantations are owned by public, industrial and non-industrial private entities with industrial ownership dominating. Even though most pine plantations in East Texas are relatively young (20 years or less), plantation information is needed for management decision-making

Research Report No. 30, A Guide for Timing Initial Tree Harvests in East Texas Loblolly and Slash Pine Plantations

In East Texas, there are approximately 3 million acres of loblolly ( Pinus taeda L. ) and slash ( Pinus elliottii Engelm. ) pine plantations. Most of these plantations, which represent about 25% of the forested area of East Texas, have been planted since 1970. As these planted trees age, East Texas foresters may be considering initial timber harvesting decisions for unthinned plantations. Often the timing of the harvests can be determined by considering combinations of economic and non-economic values, utilization standards and timber growth\u27 factors. However, in some situations, it may be appropriate to ascertain the proper timing by considerihg only timber growth factors. \u27 Decision-making models that determine the optimum timing of timber operations by maximizing a measure of economic utility, such as present net worth, provide accurate and useful information to the plantation manager. In other models, useful decisions on timing timber operations can also be obtained only by considering the development of stand factors, such as yield per acre, basal area per acre, stand height growth and stand diameter growth. The purpose of this paper is to present observed patterns of unthinned planted loblolly and slash pine diameter development and survival trends in East Texas and, based on the patterns, recommend the timing of: • An initial (or intermediate) harvest to remove only some of the planted pine trees or• An initial (or final) harvest to remove all of the planted pine trees, while realizing that the growth patterns present in some unthinned East Texas pine plantations may suggest that no immediate timber harvests may be appropriate

Community shifts and carbon translocation within metabolically-active rhizosphere microorganisms in grasslands under elevated CO₂

International audienceThe aim of this study was to identify the microbial communities that are actively involved in the assimilation of rhizosphere-C and are most sensitive in their activity to elevated atmospheric CO2 in a temperate semi-natural low-input grassland ecosystem. For this, we analyzed 13C signatures in microbial biomarker phospholipid fatty acids (PLFA) from an in-situ 13CO2 pulse-labeling experiment in the Giessen Free Air Carbon dioxide Enrichment grasslands (GiFACE, Germany) exposed to ambient and elevated (i.e. 50% above ambient) CO2 concentrations. Short-term 13C PLFA measurements at 3 h and 10 h after the pulse-labeling revealed very little to no 13C enrichment after 3 h in biomarker PLFAs and a much greater incorporation of new plant-C into fungal compared to bacterial PLFAs after 10 h. After a period of 11 months following the pulse-labeling experiment, the 13C enrichment of fungal PLFAs was still largely present but had decreased, while bacterial PLFAs were much more enriched in 13C compared to a few hours after the pulse-labeling. These results imply that new rhizodeposit-C is rapidly processed by fungal communities and only much later by the bacterial communities, which we attributed to either a fungal-mediated translocation of rhizosphere-C from the fungal to bacterial biomass or a preferential bacterial use of dead root or fungal necromass materials as C source over the direct utilization of fresh root-exudate C in these N-limited grassland ecosystems. Elevated CO2 caused an increase in the proportional 13C enrichment (relative to the universal biomarker 16:0) of the arbuscular mycorrhizal fungal biomarker PLFA 16:1?5 and one gram-positive bacterial biomarker PLFA i16:0, but a decrease in the proportional 13C enrichment of 18:1?9c, a commonly used though questionable fungal biomarker PLFA. This suggests enhanced fungal rhizodeposit-C assimilation only by arbuscular mycorrhizal fungal species under elevated CO2