Does Acidification Policy Follow Research in Northern Sweden? The Case of Natural Acidity During the 1990's

The situation in northern Sweden did not figure prominently in the intense period of research during the 1980's that laid the basis for many acidification-related policies now in effect in Europe and Sweden. Northern Sweden has not only relatively low acid deposition levels and significant sources of natural acidity, but also intense episodes of pH decline during spring flood that are a major focus of liming activity. Controversy over that liming and natural acidity has led to scientific advances. These include discovery of a correlation between sulfur in snow and the anthropogenic contribution to the subsequent spring flood ANC decline, but also that natural organic acidity is responsible for most of the spring pH decline in the region. This paper compares the developments in liming policy with the scientific developments of relevance to the region during the last decade. Considerable discrepancies are noted which create opportunities for revising remediation policies to better reflect the state of knowledge in 2000.     

Silicate mineral weathering rate estimates: Are they precise enough to be useful when predicting the recovery of nutrient pools after harvesting?

Are current estimates of silicate minerals weathering rates precise enough to predict whether nutrient pools will recover after forest harvesting? Answering this question seems crucial for sustainable forestry practices on silicate dominated soils. In this paper, we synthesize estimated Ca and K weathering rates (derived using seven different approaches) from a forested area in northern Sweden (the Svartberget-Krycklan catchment) to evaluate the precision of weathering rate estimates. The methods were: mass-balance budgets (catchment and pedon-scale); long-term weathering losses inferred from weathered soil profiles (using zirconium as a conservative tracer); strontium isotopes (⁸⁶Sr/⁸⁵Sr) as proxy for catchment export of geogenic Ca; climate based regressions; a steady-state, process-based weathering model (PROFILE) and a dynamic, conceptual catchment geochemistry model (MAGIC). The different methods predict average weathering rates of 0.67 ± 0.71 g Ca m⁻² year⁻¹ (mean ± stdev) and 0.39 ± 0.38 g K m⁻² year⁻¹, suggesting a cumulative weathering release during a forest rotation period of 100 years that is the same magnitude as losses induced by forest harvesting at the end of the period. Clearly, forestry practices have the capacity to significantly alter the long-term nutrient status of the soil and cation concentrations in soil-water runoff. However, the precision in weathering estimates are lower than that needed to distinguish between effects on nutrient pools by different forest practices (complete-tree harvesting versus conventional stem only harvest). Therefore, we argue that nutrient budgets, where weathering rates play a crucial role, cannot be used as basis for resolving whether different harvesting techniques will allow nutrient pools to recover within one rotation period. Clearly, this hampers the prerequisite for sound decision making regarding forestry practices on silicate mineral dominated soils.     

A meta-analysis of the effects of nitrogen additions on base cations: Implications for plants, soils, and streams

The dominant base cations (BC; i.e., Ca²⁺, Mg²⁺, K⁺, and Na⁺) are important in buffering soil and water acidity in both terrestrial and aquatic ecosystems. Ca²⁺, Mg²⁺, and K⁺ are also important in many plant physiological functions. Because BC availability is affected by changes in the nitrogen (N) cycle, we conducted a meta-analysis of previously published data to determine if N fertilization alters the availability of BC in terrestrial and stream ecosystems across biomes. We include data from 107 independent studies published in 62 different articles, taking a holistic perspective on BC by examining their responses to added N in plant foliage, bulk soil, soil solution, and stream water. Our results suggest N fertilization may accelerate BC loss from terrestrial ecosystems over time periods less than five years. We found that N additions resulted in an overall 24% decrease in the availability of exchangeable Ca²⁺, Mg²⁺, and K⁺ in the bulk soil of boreal forest, temperate forest, and grassland biomes. Collectively, responses of BC in boreal forest, temperate forest, tropical forest, and grassland biomes increased following N fertilization by about 71% in soil solution and 48% in stream waters. Additionally, BC responses in foliage decreased in boreal forest and temperate forest biomes following N additions over time periods less than five years, but there were no significant changes over longer time periods. Despite large short-term shifts in BC responses following N additions, we did not find evidence of widespread negative impacts on ecosystems over time periods greater than five years. This analysis suggests effects of N addition on the availability of exchangeable BC may diminish over time. Although the effects on BC can be substantial over periods less than five years, there is little available evidence that N fertilization has had large-scale detrimental effects on the availability of BC needed for plant growth within terrestrial or aquatic ecosystems.     

Magic Modeling of Long-Term Lake Water and Soil Chemistry at Abborrträsket, Northern Sweden

The geochemical model MAGIC has been applied to the Abborrträsket lake catchment in northern Sweden for the period 1843-2000. The two objectives were to 1.) simulate historical biogeochemical fluxes and pools and 2.) test whether the MAGIC model of biogeochemical cycling contradicts the published diatom record of a relatively stable pH (around 6) during the last two centuries in this weakly buffered, acid sensitive lake. Abborrträsket has received elevated sulfur and nitrogen deposition in the second half of the 20th Century and had a large part of its catchment clearcut in 1975. The MAGIC simulation of very small pH decline from 6.1 to 5.9 between 1843 and 1987 was comparable to the published diatom reconstructions of almost stable lake water pH up until the lake was limed in 1988. MAGIC also simulated the modern soil and water chemistry, including lake liming. Thus the diatom indication of stable pH cannot be dismissed as necessarily incorrect.     

Discriminating between village and commercial hunting of apes

Hunting is the major driver of large mammal decline in Central African forests. In slowly reproducing species even low hunting pressure leaves spatial gradients with wildlife density increasing with distance from transport routes and human settlements. Park management can use this pattern formation to identify sources of threats, but also to discriminate between different threat scenarios, such as the impact of subsistence vs. commercial hunting. We conducted an ape survey in the mountainous Moukalaba Doudou National Park, Gabon, to evaluate whether potential population gradients would emanate from the three human population centers in the region or the villages surrounding the park. Using generalized linear modeling we found hill slope as a good predictor of ape nest occurrence probability and the distance to human population centers a better predictor of ape nest density and ape nest group size than distance to villages. In fact ape nest density was three times lower at the park borders close to the human population centers than in the park’s interior. The results indicate that Moukalaba’s ape population is more impacted by commercial than subsistence hunting and suggest that park management should focus conservation efforts on the human population centers. We conclude that in particular for slowly reproducing species geographic information on wildlife population gradients are of additional value for guiding protected area management. The hunting impact on those species might be easily underestimated, if derived only from market surveys or transport route controls, where they are only rarely found.     

Comparing buffer zone alternatives in forest planning using a decision support system

Increased awareness of the connection between forest management activities and negative effects on water quality means that forestry needs to consider its potential impact on the aquatic environment when planning operations. Protective buffer zones are effective, but their design can vary. To be able to incorporate up-to-date scientific theory into practical applications easy-to-use planning tools are needed. In this study, we evaluate different buffer zone alternatives by using the freely available decision support system Heureka. The consequences on both economic and ecological values over a time period of 100 years were evaluated for two buffer zone approaches and three management alternatives within the buffer zones. Results indicated that there is a trade-off between economic and ecological values when managing the buffer zones. To be able to perform the analyses within Heureka, a new tool was developed. This software development provides access to a forest planning tool that can help improve nature conservation.     

Physiological stress responses in spotted wolffish (Anarhichas minor) subjected to acute disturbance and progressive hypoxia

The spotted wolffish (Anarhichas minor) is considered a promising species for coldwater aquaculture. It is a sedentary, bottom-dwelling fish which exhibits a calm and “non-stressed” behaviour in captivity. There are, however, no reports on the physiological responses to stressors in this species. In the present study we investigated primary (cortisol secretion) and secondary (glucose mobilization) responses to common aquaculture stressors like disturbance and hypoxia. Pre-stress plasma cortisol levels were within those generally considered representative for unstressed fish (~ 10 ng ml^− 1), whereas basal glucose levels were unusually low (0.3–0.4 mM). After exposure to a short, but severe disturbance challenge (emptying the tank of water for 10 min), the increase in plasma cortisol level was slow and relatively weak, reaching a peak level of 25 ng ml^− 1 4 to 8 h after disturbance. When the fish were exposed to a gradually decreasing oxygen level in the tank, a significantly elevated plasma cortisol level (35 ng ml^− 1) was seen in the fish that remained in the tank until oxygen saturation had decreased to 20% oxygen saturation after 2.5 h. However, a two-fold higher plasma cortisol level (~ 70 ng ml^− 1) was seen in all fish exposed to reduced oxygen levels (60, 40 and 20% oxygen saturation) after 3.5 h recovery in normoxic water. Plasma glucose levels showed only moderate increases (~ 70%) following disturbance and hypoxia challenges. An in vivo injection of ACTH caused a strong elevation of plasma cortisol (peak level ~ 170 ng ml^− 1), demonstrating a high capacity for interrenal steroidogenesis in the spotted wolffish. The slow and relatively weak cortisol response to stressors, and low plasma glucose levels, may relate to the sedentary lifestyle of the spotted wolffish. The stress-response is characterised by a passive (reactive) coping style, which is considered adaptive for farming of this species.