Trophic structure of macro- and meso-invertebrates in Japanese coniferous forest: Carbon and nitrogen stable isotopes analyses

Few studies have been published on the feeding ecology of Japanese soil fauna based on stable isotope analysis. Therefore, the present work aims to use this technique for studying the trophic structure of Japanese soil fauna at two coniferous forests. Significant differences were observed between investigated sites (Arahama and Gamo) in genus richness and abundance, while for Shannon diversity indexes the difference was non-significant. The isotopic signatures (δ¹³C and δ¹⁵N) of the invertebrates collected at Arahama ranged from 0.3 to 6.3‰ for δ¹⁵N and from −27.3 to −23.3‰ for δ¹³C. At Gamo, invertebrates δ¹³C values ranged from −26.1 to −23.5‰ and δ¹⁵N values ranged from 1.6 to 6.8‰. At both sites, invertebrates formed two distinct groups on the basis of combined C and N stable isotope ratios. The locations of these groups related to δ¹³C values. The less enriched group (δ¹³C < −25‰) and the more enriched one (δ¹³C > −25‰). The range of δ¹⁵N for the present animals exceeded two trophic levels. While, the gradual ¹⁵N enrichment within the invertebrates species may indicate the dominance of omnivory in soil food webs. The differences between sites in δ¹⁵N confirm the importance of studying the trophic structure of soil fauna locally.     

δC, δN, carbon, nitrogen and phosphorus as indicators of plant ecophysiology and organic matter pathways in Everglades deep slough, Florida, USA

Historically, the Florida Everglades was characterized by a corrugated landscape of shorter hydroperiod, elevated sawgrass (Cladium jamaicense) ridges and longer hydroperiod, deep water slough communities. Drainage and compartmentalization of the Everglades have fundamentally altered this pattern, and sawgrass ridge communities have expanded at the expense of deep water slough communities throughout much of the landscape. In this study we provide a simple isotopic and nutrient characterization of major components of the slough ecosystem to elucidate physiological and nutrient differences among species and to suggest pathways for organic matter decomposition that contribute to peat development in deep water sloughs. We examined carbon (C) and nitrogen (N) isotopes and C, N and phosphorus (P) concentrations of the floating-leaved macrophytes Nymphaea odorata and Nymphoides aquatica, the emergent macrophyte Eleocharis elongata, and the submerged species Utricularia foliosa and Utricularia purpurea, as well as soil and flocculent material from the southern Water Conservation Area 3-A. Flocculent material and soils had the highest N content (4.5 ± 0.2%) and U. foliosa and N. odorata had the highest P content (0.13 ± 0.01% to 0.12 ± 0.01%). The range for δ¹⁵N average ± SE values was 5.81 ± 0.29‰ (U. foliosa) to −1.84 ± 0.63‰ (N. odorata), while the range for δ¹³C values was −23.83 ± 0.12‰ (N. odorata) to −29.28 ± 0.34‰ (U. purpurea). Differences of up to 10‰ in C isotopic values of U. foliosa and N. odorata suggest fundamental physiological differences between these species. Along a degradation continuum, enrichment of ¹³C and ¹⁵N and extent of decomposition was negatively related to phosphorus concentrations. A two end-member ¹³C mixing model suggested that Utricularia species were the primary organic source for flocculent materials, whereas organic matter derived from root decomposition of N. odorata contributed to the progressively enriched δ¹³C values found with depth in soils. These results illustrate the fundamentally important roles of Nymphaea and Utricularia species in ecosystem dynamics of deep water sloughs.     

Stable carbon and nitrogen isotope discrimination in soft tissues of the leatherback turtle (Dermochelys coriacea): Insights for trophic studies of marine turtles

The trophic ecology of marine vertebrates has been increasingly studied via stable isotope analysis of body tissues. However, the theoretical basis for using stable isotopes to elucidate consumer–prey relationships remains poorly validated for most taxa despite numerous studies using this technique in natural systems. In this study, we measured stable carbon and stable nitrogen diet-tissue discrimination (Δ_dt) in whole blood, red blood cells, blood plasma solutes, and skin of leatherback sea turtles (Dermochelys coriacea; N = 7) maintained in captivity for up to 424 days and fed an isotopically consistent control diet with a mean C:N ratio of 2.94:1.00 and an energetic content of 20.16 ± 0.39 kJ g^− 1 Dry Mass. We used a random-effect repeated measure model to evaluate isotopic consistency among tissue samples collected on days 276, 348, and 424. Both δ¹³C and δ¹⁵N remained consistent among sampling events in all tissues (all 95% posterior intervals for the slopes of a linear model included zero), indicating that all tissues had fully integrated diet-derived stable isotope compositions. Mean tissue-specific δ¹³C ranged from − 18.30 ± 0.16‰ (plasma solutes) to − 15.54 ± 0.14‰ (skin), whereas mean δ¹⁵N was from 10.06 ± 0.22‰ (whole blood) to 11.46 ± 0.10‰ (plasma solutes). The computed Δ_dt factors for carbon ranged from − 0.58‰ (plasma solutes) to + 2.25‰ (skin), whereas Δ_dt for nitrogen was from + 1.49 (red blood cells) to + 2.85 (plasma solutes). As the only discrimination factors available for leatherback turtles, our data will be useful for future interpretations of field-derived stable isotope data for this species. The inherent variability in Δ_dt values among individuals was low, which supports the value of these data for dietary reconstructions. However, it is important to note that tissue-specific discrimination factors for leatherbacks contrast with the widely accepted values for endothermic species (0–1‰ for C, 3–5‰ for N), and are also different from values established for hard-shelled turtles. This underscores the need for species- and tissue-specific discrimination factors before interpreting trophic studies of wild animals, including marine turtles.     

Resource use by salmonids in riverine,lacustrine and marine environments: Evidence from stable isotope analysis

Synopsis We measured stable isotope ratios (δ¹³C and δ¹⁵N) of invertebrates, Atlantic salmon, Salmo salar, and brook trout, Salvelinus fontinalis, in three distinct freshwater environments (headwater tributary, ultra-oligotrophic lake, and main-stem river) in the Western Brook system, Newfoundland, Canada. Large differences in the stable carbon signatures of invertebrates allowed the identification of organic matter assimilation from each environment by resident parr and migrating smolts. Brook trout captured in the headwater tributary in June had a carbon signature characteristic of the tributary, while those collected in August had enriched ¹³C (maximum = −15.6‰) and ¹⁵N (maximum = 12.8‰) values. These enriched carbon and nitrogen signatures were indicative of foraging at sea. There was a low correlation between δ¹³C and δ¹⁵N (r² = 0.198) for individual fish that was likely due to the confounding influence of trout feeding in the lake and the lower main-stem of the river, where δ¹³C of food sources was high but δ¹⁵N was low. Smolts emigrating from Western Brook Pond where they had been foraging (based on lacustrine carbon signatures) were significantly larger than those emigrating from a nursery brook and the main river in the same basin, despite having the same median age. These results suggest better growth opportunities in the lake environment. Trout fork length was positively correlated with δ¹³C and δ¹⁵N, demonstrating that larger individuals had been feeding outside the brook. These results support previous studies that found increased growth potential for salmonids in lacustrine and marine environments, and further, indicate possible adaptive advantages for salmonid movement away from natal brooks.     

Specific growth rate as a determinant of the carbon isotope composition of the temperate seagrass Zostera marina

The seasonal variability of specific growth rate and the carbon stable isotope ratio (δ¹³C) of leaf blades (δ¹³C_leaf) of a temperate seagrass, Zostera marina (within 10 days old) were measured simultaneously, together with the δ¹³C of dissolved inorganic carbon (δ¹³C_DIC) at three sites in the semi-closed Akkeshi estuary system, northeastern Japan, in June, September, and November 2004. The δ¹³C_leaf ranged from −16.2 to −6.3‰ and decreased from summer to winter. The simultaneous measurement of the δ¹³C_leaf, growth rate, and morphological parameters (mean leaf length and width, mean number of leaves per shoot, and sheath length) of the seagrass and δ¹³C_DIC in the surrounding water allowed us to compare directly the δ¹³C_leaf and specific growth rate of seagrass. The difference in the δ¹³C of seagrass leaves relative to the source DIC (Δδ¹³C_{leaf − DIC}) was the least negative (−11 to −7‰) in June at all three sites and became more negative (−17 to −8‰) as the specific growth rate decreased. This positive correlation between Δδ¹³C_{leaf − DIC} and specific growth rate can be used to diagnose the growth of seagrasses. Δδ¹³C_{leaf − DIC} changed by −1.7 ± 0.2‰ when the leaf specific growth rate decreased by 1% d⁻¹.     

Depleted methane-derived carbon in waters of Lake Baikal,Siberia

Results of hydrochemical and stable isotope measurements during the ice-breaking period on Lake Baikal indicate an apparent lack of relationship between measured δ¹³C of dissolved inorganic carbon (DIC) and phytoplankton below the trophogenic layer. While planktonic values of −31.7 to −33.5‰ are within a typical lacustrine range, the δ¹³C values of DIC turned out to be very negative, from −28.9 to −35.6‰. These isotopic values of DIC appear to be associated with oxidation of methane that accumulated during winter ice cover period. At the time of sampling, however, the observed depletion did not affect the phytoplankton/DIC fractionation relationship, because the difference between phytoplankton and DIC (−20 to −22‰ in surface waters) lies within the expected range of the fractionation coefficient. By analogy with small lakes, we explain this lack of relationship by the time lag between peak productivity and peak methane oxidation. Our interpretation of the Baikal DIC isotopic signature is consistent with methanogenesis in bottom sediments and with the known presence of widespread unstable gas hydrates and active methane seeps on the lake floor. Our findings suggest that methane is an important component of the Baikal carbon cycle, that late winter concentrations of methane in Baikal under ice may be 3–4 orders of magnitude higher than previously reported values for summer, and that the lake may be emitting a significant amount of methane to the atmosphere.     

Macroalgal blooms on southeast Florida coral reefs: II. Cross-shelf discrimination of nitrogen sources indicates widespread assimilation of sewage nitrogen

Since 1990, coral reefs off southeast Florida have experienced an unprecedented succession of macroalgal blooms and invasions. To determine if anthropogenic land-based nitrogen (N) sources support these HABs, we collected macroalgal tissue for stable nitrogen isotope (δ¹⁵N) analysis at three spatially distinct depths ranging from the shallow subtidal to the shelf break (43 m) along seven transects from Jupiter to Deerfield Beach, Florida, USA. This sampling was initiated during a historically significant drought in the spring of 2001 when rainfall, stormwater runoff, and upwelling were at a minimum. The sampling was repeated in the summer wet season following significant stormwater runoff and during a strong upwelling event.Despite significant seasonal changes in N source availability, δ¹⁵N values did not vary between samplings. Collectively, δ¹⁵N values were significantly higher on inshore shallow reefs (+8.1‰) compared to mid (+6.1‰) and deep reefs (+6.7‰). Values were also elevated in the southern portion of the study area (e.g., Boca Raton, +8.5‰) where nearly 1.5 billion l/day of secondarily treated wastewater is discharged into the ocean via coastal outfalls. Codium isthmocladum, a macroalga that assimilates its nutrients entirely from the water column, was the dominant bloom species in the southern study area, where tissue δ¹⁵N values matched source values of nearby sewage outfalls. The northern study area was dominated by species of the genus Caulerpa, particularly the invasive Pacific native C. brachypus var. parvifolia, which are capable of accessing benthic nutrient sources (e.g., submarine groundwater discharge, SGD) by means of root-like rhizoids. The northern area does not have sewage outfalls but features a highly transmissive geologic zone where SGD may be enriched with septic tank leachate and effluent from municipal deep injection wells.Multiple lines of evidence supported the hypothesis that land-based sewage N was more important than upwelling as a N source to these HABs: (1) δ¹⁵N values were highest on shallow reefs and decreased with increasing depth, indicating land-based sources of enrichment; (2) elevated δ¹⁵N values occurred in these HABs during the dry season, prior to the onset of the summer upwelling; (3) elevated NH₄⁺ concentrations occur on these reefs during both upwelling and non-upwelling periods and are kinetically preferred by macroalgae compared to upwelled NO₃⁻. These findings provide a case study of a coupling between increasing anthropogenic activities and the development of macroalgal HABs, including invasive species that threaten economically important reef resources in southeast Florida.     

Diet and physiological responses of Spondyliosoma cantharus (Linnaeus, 1758) to the Caulerpa racemosa var. cylindracea invasion

Marine invasions are a worldwide problem that involves changes in communities and the acclimation of organisms to them. The invasive Chlorophyte Caulerpa racemosa var. cylindracea is widespread in the Mediterranean and colonises large areas from 0 to 70 m in depth. The omnivorous fish Spondyliosoma cantharus presents a high frequency of occurrence of C. racemosa in the stomach contents at invaded areas (76.3%) while no presence of C. racemosa was detected in control areas. The isotopic composition of muscle differed significantly between invaded and non-invaded sites for δ¹³C (− 16.67‰ ± 0.09 and − 17.67‰ ± 0.08, respectively), δ¹⁵N (10.22‰ ± 0.22 and 9.32‰ ± 0.18, respectively) and the C:N ratio (2.01 ± 0.0002 and 1.96 ± 0.009, respectively). Despite the high frequency of occurrence of C. racemosa in the stomach contents of S. cantharus and its important contribution to the δ¹³C source (20.7% ± 16.2), the contribution of C. racemosa to the δ¹⁵N in S. cantharus food sources was very low (6.6% ± 5.8). Other invertebrate prey such as decapods and polychaetes were more important contributors to the δ¹⁵N source at both invaded and non-invaded sites. Activation of enzymatic pathways (catalase, superoxide dismutase, glutathione-s-tranferase, 7-ethoxy resorufin O-de-ethylase) but not a significant increase in lipid peroxidation MDA (0.49 ± 0.01 nmol/mg prot at non-invaded and 0.53 ± 0.01 nmol/mg prot at invaded sites) was observed in S. cantharus individuals living in C. racemosa-invaded sites compared with control specimens. The low δ¹⁵N contribution values of C. racemosa by S. cantharus together with the toxicity demonstrated by the activation of the antioxidant defences and the important contribution of invertebrate prey to the δ¹⁵N could mean that the ingestion of C. racemosa by S. cantharus might be unintentional during the predation of invertebrate preys living underneath the entanglement of the C. racemosa fronds and stolons mats.     

Mangrove ecosystem changes during the Holocene at Spanish Lookout Cay, Belize

Mangroves are halophytic plants living at the land–sea interface and are therefore natural trackers of sea-level. Multiple proxies of a continuous (8 m) mangrove peat core (BT-79) from Spanish Lookout Cay, Belize illustrate mangrove ecosystem changes during the Holocene. Radiocarbon measurements show this site was colonized by mangroves ~ 8000 cal. yrs BP, with a significant decrease in the peat accumulation rate from ~ 6000 to 1000 cal. yrs BP. Stratigraphic characteristics of this peat core such as bulk density, magnetic susceptibility, and loss on ignition show relative uniformity, inferring an uninterrupted mangrove ecosystem during a majority of the Holocene. This is supported by pollen data from BT-79 that show that the site has been consistently dominated by Rhizophora mangle (red mangrove), with Avicennia germinans (black mangrove) and Laguncularia racemosa (white mangrove) present as well. Subfossil R. mangle leaves are used for stable nitrogen, carbon, and oxygen isotope (δ¹⁵N, δ¹³C, and δ¹⁸O) analyses. δ¹⁵N and δ¹³C values provide a proxy of this plant's past physiology and stand structure showing that dwarf (δ¹⁵N < − 3‰) and tall (δ¹³C < − 27‰) R. mangle stands were previously present at the site, which are a result of nutrient limitations that we equate with seawater inundation. δ¹⁸O values show differences in source water of R. mangle, with higher values attributed to the source water being composed of a greater proportion of seawater relative to precipitation. A decrease in inundation at the site is shown by lower δ¹⁸O values (< 19‰) from ~ 7000 to ~ 1000 cal. yrs BP that covary with the decreased sedimentation rate. Existing Caribbean sea-level data do not show evidence of a decrease in the rate of relative sea-level rise or fluctuations that we take to be the major causes of environmental changes at site BT-79.     

Variation in δC values for the seagrass Thalassia testudinum and its relations to mangrove carbon

Carbon isotope ratios (¹³C/¹²C) were measured for the leaves of the seagrass Thalassia testudinum Banks ex König and carbonates of shells collected at the seagrass beds from seven sites along the coast of southern Florida, U.S.A. The δ¹³C values of seagrass leaves ranged from −7.3 to −16.3‰ among different study sites, with a significantly lower mean value for seagrass leaves from those sites near mangrove forests (−12.8 ± 1.1‰) than those far from mangrove forests (−8.3 ± 0.9‰; P < 0.05). Furthermore, seagrass leaves from a shallow water area had significantly lower δ¹³C values than those found in a deep water area (P < 0.01). There was no significant variation in δ¹³C values between young and mature leaves (P = 0.59) or between the tip and base of a leaf blade (P = 0.46). Carbonates of shells also showed a significantly lower mean δ¹³C value in the mangrove areas (−2.3 ± 0.6‰) than in the non-mangrove areas (0.6 ± 0.3‰; P <0.025). In addition, the δ¹³C values of seagrass leaves were significantly correlated with those of shell carbonates (δ¹³C seagrass leaf = −9.1 + 1.3δ¹³C shell carbonate (R² = 0.83, P < 0.01)). These results indicated that the input of carbon dioxide from the mineralization of mangrove detritus caused the variation in carbon isotope ratios of seagrass leaves among different sites in this study.     

Spatial variability of stable carbon and nitrogen isotope ratios in a Mediterranean coastal lagoon

Exploring the trophic pathway of organic matter within the Mauguio lagoon (southern France, western Mediterranean), we found spatial differences in the isotopic composition (both δ¹³C and δ¹⁵N values) of organic matter sources (primary producers, particulate and sedimentary organic matter), which were mirrored in the upper trophic levels (invertebrates and fish). On average, δ¹³C was heavier by about 1.5–2‰ in the location under marine influence than in the sites influenced by freshwater discharge. The opposite trend was found for δ¹⁵N, which attained maximum values in the north-central zone influenced by freshwater delivery. For both C and N stable isotope ratios, the highest spatial variability was found in organic matter sources (2–3‰), while invertebrates and fish exhibited less variability (\~1–2‰). The differences observed may be related to both anthropogenic (wastewater input) and natural (marine vs. terrestrial inputs) factors. Discharge of wastewater, which affects the innermost location, generally determines an increase in the relative abundance of ¹⁵N. In addition, terrestrially derived nutrients and organic matter, which also affect the innermost location, are known to determine a shift towards ¹³C-depleted values. Our results substantiate the finding that the analysis of carbon and nitrogen stable isotopes can help in elucidating origin and fate of organic matter in coastal lagoons, which are characterised by a great spatial variability and complexity.     

The formation of giant tubular concretions triggered by anaerobic oxidation of methane as revealed by archaeal molecular fossils (Lower Eocene, Varna, Bulgaria)

Impressive, several meters high tubular concretions in shallow marine calcareous sands and sandstones represent part of the well-exposed, subsurface plumbing network of an Early Eocene methane seep system in the Balkanides foreland (Pobiti Kamani area, Varna, NE Bulgaria). An integrated approach, including petrography, inorganic geochemistry and lipid biomarker analyses was used to reconstruct the evolution of pore fluids and cementation conditions during tube formation and particularly, the role of methane-related carbonate diagenesis. Host sediment lithification from marine pore waters was perturbed soon after deposition by oxidation of predominantly microbial methane causing pervasive cementation by a ¹³C-poor, homogeneous calcite cement (δ¹³C values as low as − 44.5‰ V-PDB). The importance of microbially mediated anaerobic oxidation of methane (AOM) is confirmed by extremely ¹³C-depleted archaeal biomarkers (δ¹³C values as low as − 123‰ V-PDB). A suite of macrocyclic dialkyl glycerol diethers (MDGD-0 to -2) and sn-3-hydroxyarchaeol comprises a characteristic trait of the Eocene tubular concretions and might represent molecular fossils of so far unknown methane-oxidizing archaea (ANME). Subsurface calcite cementation surrounding the ascending methane plume, resulted from the changing pore water chemistry in response to AOM and could have, on a local scale, been encouraged by the concurrent alteration of detrital feldspar. Fluctuating δ¹³C (up to − 8‰ V-PDB) and δ¹⁸O (− 0.5 to − 9‰ V-PDB) signatures within a single tubular sandstone concretion are at least partly the consequence of isotopic resetting during late meteoric water circulation.     

Climatic and local effects on stalagmite δC values at Lianhua Cave, China

Carbon isotopes in speleothems may serve as indicators of vegetative change, climatic conditions, and karst processes. In many recent studies of Chinese stalagmites, however, carbon isotopes have often been neglected or underutilized in interpreting paleoenvironments. Here, we present a continuous decadal-scale δ¹³C record (819 measurements) of the mid- to late-Holocene from a precisely-dated (10 ²³⁰Th dates) aragonite stalagmite from Lianhua Cave, Hunan Province, China. Compared to coeval stalagmites from other Chinese caves, the average δ¹³C value (− 3.6‰) of stalagmite A1 is higher by ~ 2–7‰. Variations in the δ¹³C values (0.1‰ to − 6.0‰) reflect changes in both vegetative productivity and inorganic processes, which respond to climatic processes. The δ¹³C record of stalagmite A1 can be subdivided into three intervals: 1) warm–humid stage (6.6 to 3.8 ka); 2) transitional stage (3.8 to 1.6 ka); and 3) cool–arid stage (1.6 ka to present). Comparisons with other stalagmite and paleoclimatic records demonstrate that these intervals are generally consistent with changes in regional vegetation and climatic conditions.     

Carbon and nitrogen in a temperate agroforestry system: Using stable isotopes as a tool to understand soil dynamics

Natural exchanges of carbon (C) between the atmosphere, the oceans, and terrestrial ecosystems are currently being modified through human activities as a result of fossil fuel burning and the conversion of tropical forests to agricultural land. These activities have led to a steady increase of atmospheric carbon dioxide (CO₂) over the last two Centuries. The goal of this study was to determine the potential of temperate agroforestry systems to sequester C in soil. Therefore, changes in the soil organic C (SOC) and nitrogen (N) pools were quantified and the δ¹³C and δ¹⁵N stable isotope technique was applied to assess soil C and N dynamics in a 13-year old hybrid poplar alley cropping system in Southern Canada. Results from this study showed that after 13 years of alley cropping the SOC and N pools did not differ significantly (p = 0.01) with distance from the tree row, although a trend of a larger SOC and N pool near the tree row could be observed. Soil organic C after 13 years of alley cropping, was 19 mg C g⁻¹ compared to 11 mg C g⁻¹ upon initiation of agroforestry. Soil organic C and N were not evenly distributed throughout the plow layer. The largest C and N pool occurred in the top 20 cm, which is due to the accumulation of organic material in the upper horizons as a result of no-till cultivation. The entire soil, to a 40 cm depth, showed a δ¹³C shift to that of C₃ residue. This shift reflects the greater input of residues from C₃ plants such as that derived from beans, wheat, and hybrid poplar leaf litterfall. The proportion of C derived from a C₃ source ranged from 64 to 69% to a 40 cm depth. The soil δ¹⁵N signature of this study is similar to that of mineral soil, and reflect values characteristic of N mineralization processes. However, the entire soil shows a positive shift in δ¹⁵N as a result of historical additions of manure and current use of mineral fertilizers, and ongoing processes of denitrification and nitrate leaching, which leads to an enrichment of the soil.     

The humus layer determines SO<Subscript>4</Subscript><Superscript>2−</Superscript> isotope values in the mineral soil

Biocycling of sulfur (S) has been proposed to play an important role in the recovery of ecosystems following anthropogenic S deposition. Here, we investigated the importance of the humus layer in the biocycling of S in three forested catchments in the Gårdsjön area of southwestern Sweden with differing S inputs and S isotope signature values. These experimental sites consisted of two reference catchments and the Gårdsjön roof experiment catchment (G1), where anthropogenic deposition was intercepted from 1991 until May 2002 by a roof placed over the entire catchment area. Under the roof, controlled levels of deposition were applied, using a sprinkler system, and the only form of S added was marine SO₄²⁻ with a δ of +19.5‰.We installed ion exchange resin bags at the interface between the humus layer and mineral soil at each of the catchments to collect SO₄²⁻ passing through the humus. The resin bags were installed on four occasions, in 1999 and 2000, covering two summer and two winter periods. The ions collected by each bag during these sampling periods were then eluted and their δ values and SO₄²⁻ concentrations determined. The most striking result is that the average δ value in the resin bags was more than 12‰ lower compared to that of the sprinkler water in the G1 roof catchment. There was no increasing trend in the isotope value in the resin bag SO₄²⁻ despite that the roof treatment has been on-going for almost 10 years; the average value for all resin bags was +7.1‰. The highest δ values found in the G1 roof catchment were between +11‰ and +12‰. However, these values were all obtained from resin bags installed at a single sampling location. Throughfall and resin bag δ values were more similar in the two reference catchments: about +7.5‰ in both cases. There was, however, an increase in resin bag δ values during the first winter period, from about +7‰ to +9‰. The resin bag δ value was linearly and positively related (r² = 0.26, p < 0.001) to the amount of SO₄²⁻ extracted from the resin bags, if relatively high amounts (>50 mmol m⁻²) were excluded. High amounts of resin bag SO₄²⁻ seemed to be related to groundwater inputs, as indicated by the δ value. Our results suggest that rapid immobilization of SO₄²⁻ into a large organic S pool may alter the S isotope value and affect the δ values measured in the mineral soil and runoff.     

Drift rhodophyte blooms emerge in Lee County, Florida, USA: Evidence of escalating coastal eutrophication

Macroalgal blooms have increased globally in recent decades as a result of increased nutrient enrichment and eutrophication of coastal waters. In Lee County, Florida, this problem reached a critical stage in 2003/2004 when massive rhodophyte blooms washed ashore, making beaches unsuitable for recreation and requiring an expensive removal program. To better understand the ecology of these blooms, water quality and macroalgae sampling was conducted in August 2004, prior to hurricane Charley, and again in late October following several months of large freshwater discharges from the Caloosahatchee River. During both samplings, water and macroalgae were collected along a gradient extending from the Caloosahatchee River to natural and artificial reefs up to 26 km from shore.Dissolved nutrient concentrations were generally high throughout the study area, with significantly higher concentrations in the Caloosahatchee River. Mean dissolved inorganic nitrogen concentrations in the Caloosahatchee River increased from Ortona Lock (<18 μM) to Franklin Lock (23–28 μM) downstream during both samplings, indicating significant enrichment within the basin. On coastal reefs, mean ammonium concentrations increased six-fold (≤0.20–1.31 μM) and soluble reactive phosphorus increased three-fold (0.30–0.92 μM) from August to October, respectively. Mean reef macroalgae C:N ratios were low and similar in August (13.9) and October (13.5), and C:P and N:P ratios were also low but decreased significantly from August to October (386–242 and 27.4–17.5, respectively). Macroalgal δ¹⁵N values increased from Ortona Lock (+8 to 9‰) to Franklin Lock (+12 to 15‰) during both samplings, were within the sewage nitrogen range, and decreased with increasing distance from shore to +3.0‰ at the most offshore reef. Macroalgae (Gracilaria, Hypnea, Botryocladia, Eucheuma, Sargassum) collected in July 2004 from Lee County beaches had mean δ¹⁵N values >+6.0‰, similar to values for macroalgae on inshore reefs and within the sewage nitrogen range. However, mean δ¹⁵N values of reef macroalgae decreased from August (+5.84‰) to October (+3.89‰) as Caloosahatchee River discharges increased, suggesting relatively larger contributions from nitrogen sources with low δ¹⁵N values (<+3‰), such as rainfall and agricultural fertilizers, in the wet season. Improved management of freshwater releases from Lake Okeechobee, combined with nutrient removal from sewage effluent within the Caloosahatchee River drainage basin, could help mitigate future macroalgal blooms in Lee County's coastal waters.     

Remediation of depleted soils by addition of ion exchange resins

Parallel investigations with fertility were carried out in standard garden soil with ion exchange substrate BIONA 111 as well with mixtures in different proportions. The ion exchange substrate was a mixture of ion exchange resins saturated in certain proportions with a complete set of biogenic ions. Plant productivity in the ion exchange substrate in a 6-week vegetation period was 950 g/kg of the green biomass compared with 29 g/kg in soil. Productivity linearly depended on the mass fraction of the ion exchange substrate in the mixtures with the garden soil. Addition of 1% of the ion exchange substrate is sufficient for starting vegetation in completely depleted soil and barren sand. Addition of different ionic forms of ion exchange resins (K⁺, Ca²⁺+Mg²⁺+K⁺, NO₃⁻, NO₃⁻+H₂PO₄²⁻+SO₄²⁻) caused pronounced positive effects on soil productivity though these effects were less significant than those of ion exchange substrate. Addition of ion exchange substrates can be an efficient means for remediation of destroyed soils and fruitless rocks.     

Comparison of stable-carbon isotope composition in the growth rings of Isorberlinia doka, Daniella oliveri, and Tamarindus indica and West African climate

Inter-ring variations in stable-carbon isotope composition of cellulose in Daniella oliveri, Isoberlinia doka, and Tamarindus indica stumps were analyzed for nine trees in the Soudan-Sahel zone of West Africa. This pioneer isotopic study is a contribution to on-going efforts to evaluate the feasibility of extracting proxy climatic records from tree-rings in this area. Our aim is to investigate trends in individual floating δ¹³C time series to assess if patterns in variability within and between rings are consistent with those in other climatically sensitive tree-ring δ¹³C series. Samples were collected primarily from tree stumps but kill dates were unknown. Tree age was estimated from stump condition and shoot regrowth. This approach, combined with low sample replication, hindered the establishment of absolute dates. Nevertheless, δ¹³C and discrimination (Δ¹³C), absolute values and variability in the time series are similar to those often seen in tree-rings. Average δ¹³C values for individual series range from −25.90‰ to −23.72‰ and average Δ¹³C values from 16.56‰ to 18.99‰. It is well known that seasonal rainfall is inversely related to the δ¹³C in growth-season-dry environments and positively covaries with Δ. We investigate the possibility of using this relationship to temporally anchor the time series and to identify missing and false rings in wood segments with indistinct growth. The variability in these time series is consistent with expected patterns and shows promise for facilitating the development of stable carbon isotope tree-ring chronologies for West Africa.     

Land treatment of olive oil mill wastewater

Experiments carried out in lysimeters filled with two calcareous clayey soils (ca 40% CaCO₃; ca 40% clay), showed that a 2m layer of soil almost completely removed the organic and inorganic components of olive oil mill wastewater (OMW) when it was applied in doses of 5000–10000m³ha⁻¹year⁻¹. This efficiency was maintained for at least 2 years. In field experiments, the application of OMW to one of these soils during three successive years at an annual rate of up to 6000m³ha⁻¹ caused changes in some chemical properties of the soil, especially in the upper layer (0–50cm). Concentrations of soil organic matter, Kjeldahl N, soluble NO₃ and available P increased enhancing soil fertility. On the other hand, soil electrical conductivity and sodium adsorption ratio also increased but below the levels representing salinization or sodification hazard for the soil. Furthermore, leaching of Na⁺ and NO₃⁻ below the 1 m layer were detected.     

Effects of spawning Pacific salmon on terrestrial invertebrates: Insects near spawning habitat are isotopically enriched with nitrogen‐15 but display no differences in body size

When Pacific salmon (Oncorhynchus spp.) spawn and die, they deliver marine‐derived nutrient subsidies to freshwater and riparian ecosystems. These subsidies can alter the behavior, productivity, and abundance of recipient species and their habitats. Isotopes, such as nitrogen‐15 (¹⁵N), are often used to trace the destination of marine‐derived nutrients in riparian habitats. However, few studies have tested for correlations between stable isotopes and physiological responses of riparian organisms. We examined whether increases in δ ¹⁵N in terrestrial insect bodies adjacent to salmon spawning habitat translate to changes in percent nitrogen content and body size. This involved comparisons between distance from a salmon‐bearing river, marine‐derived nutrients in soils and insects, soil moisture content, and body size and nitrogen content in two common beetle families (Coleoptera: Curculionidae, Carabidae). As predicted, δ¹⁵N in riparian soils attenuated with distance from the river but was unaffected by soil moisture. This gradient was mirrored by δ¹⁵N in the herbivorous curculionid beetles, whereas carabid beetles, which feed at a higher trophic level and are more mobile, did not show discernable patterns in their δ¹⁵N content. Additionally, neither distance from the river nor body δ¹⁵N content was related to beetle body size. We also found that nitrogen‐15 was not correlated with total percent nitrogen in insect bodies, meaning that the presence of spawning salmon did not increase the percent nitrogen content of these insects. We conclude that while salmon‐derived nutrients had entered terrestrial food webs, the presence of δ¹⁵N alone did not indicate meaningful physiological changes in these insects in terms of percent nitrogen nor body size. While stable isotopes may be useful tracers of marine‐derived nutrients, they cannot necessarily be used as a proxy for physiologically important response variables.