Impacts of an Invasive Snail (Tarebia granifera) on Nutrient Cycling in Tropical Streams: The Role of Riparian Deforestation in Trinidad, West Indies

Non-native species and habitat degradation are two major catalysts of environmental change and often occur simultaneously. In freshwater systems, degradation of adjacent terrestrial vegetation may facilitate introduced species by altering resource availability. Here we examine how the presence of intact riparian cover influences the impact of an invasive herbivorous snail, Tarebia granifera, on nitrogen (N) cycling in aquatic systems on the island of Trinidad. We quantified snail biomass, growth, and N excretion in locations where riparian vegetation was present or removed to determine how snail demographics and excretion were related to the condition of the riparian zone. In three Neotropical streams, we measured snail biomass and N excretion in open and closed canopy habitats to generate estimates of mass- and area-specific N excretion rates. Snail biomass was 2 to 8 times greater and areal N excretion rates ranged from 3 to 9 times greater in open canopy habitats. Snails foraging in open canopy habitat also had access to more abundant food resources and exhibited greater growth and mass-specific N excretion rates. Estimates of ecosystem N demand indicated that snail N excretion in fully closed, partially closed, and open canopy habitats supplied 2%, 11%, and 16% of integrated ecosystem N demand, respectively. We conclude that human-mediated riparian canopy loss can generate hotspots of snail biomass, growth, and N excretion along tropical stream networks, altering the impacts of an invasive snail on the biogeochemical cycling of N

Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed

Anthropogenic nitrogen pollution is a critical problem in freshwaters. Although riverbeds are known to attenuate nitrate, it is not known if large woody debris (LWD) can increase this ecosystem service through enhanced hyporheic exchange and streambed residence time. Over a year, we monitored the surface water and pore water chemistry at 200 points along a ~50m reach of a lowland sandy stream with three natural LWD structures. We directly injected 15N-nitrate at 108 locations within the top 1.5m of the streambed to quantify in situ denitrification, anammox and dissimilatory nitrate reduction to ammonia, which, on average, contributed 85%, 10% and 5% of total nitrate reduction, respectively. Total nitrate reducing activity ranged from 0-16µM h-1 and was highest in the top 30cm of the stream bed. Depth, ambient nitrate and water residence time explained 44% of the observed variation in nitrate reduction; fastest rates were associated with slow flow and shallow depths. In autumn, when the river was in spate, nitrate reduction (in situ and laboratory measures) was enhanced around the LWD compared with non-woody areas, but this was not seen in the spring and summer. Overall, there was no significant effect of LWD on nitrate reduction rates in surrounding streambed sediments, but higher pore water nitrate concentrations and shorter residence times, close to LWD, indicated enhanced delivery of surface water into the streambed under high flow. When hyporheic exchange is too strong, overall nitrate reduction is inhibited due to short flow-paths and associated high oxygen concentrations

Variability in organic carbon reactivity across lake residence time and trophic gradients

The transport of dissolved organic carbon from land to ocean is a large dynamic component of the global carbon cycle. Inland waters are hotspots for organic matter turnover, via both biological and photochemical processes, and mediate carbon transfer between land, oceans and atmosphere. However, predicting dissolved organic carbon reactivity remains problematic. Here we present in situ dissolved organic carbon budget data from 82 predominantly European and North American water bodies with varying nutrient concentrations and water residence times ranging from one week to 700 years. We find that trophic status strongly regulates whether water bodies act as net dissolved organic carbon sources or sinks, and that rates of both dissolved organic carbon production and consumption can be predicted from water residence time. Our results suggest a dominant role of rapid light-driven removal in water bodies with a short water residence time, whereas in water bodies with longer residence times, slower biotic production and consumption processes are dominant and counterbalance one another. Eutrophication caused lakes to transition from sinks to sources of dissolved organic carbon. We conclude that rates and locations of dissolved organic carbon processing and associated CO2 emissions in inland waters may be misrepresented in global carbon budgets if temporal and spatial reactivity gradients are not accounted for

Dose escalated simultaneous integrated boost radiotherapy for women treated by breast conservation surgery for early breast cancer: 3-year adverse effects in the IMPORT HIGH trial (CRUK/06/003)

Meeting abstract (Abstract GS4-05 from 2018 San Antonio Breast Cancer Symposium; December 4-8, 2018; San Antonio, Texas)

The effects of Ginkgo biloba extract (GBe) on axonal transport microvasculature and morphology of sciatic nerve in streptozotocin-induced diabetic rats

To evaluate the protective effects ofGinkgo biloba extract (GBe) which has antioxidant activity against peripheral neuropathy due to diabetes mellitus, slow axonal transport and morphology of sciatic nerve including endoneurial microvessels were examined in 12 rats with diabetes mellitus induced by streptozotocin (STZ, 60mg/kg, b.w., i.p.). Six of the diabetic rats were treated with 0.1 % of GBe for 6 weeks from one week after the STZ injection. Serum glucose and lipid peroxide levels in GBe-treated diabetic rats were significantly lower than those in untreated diabetic rats (p<0.01, respectively), though the serum glucose level was higher than that in the control rats. L-[35S] methionine pulse radiolabeling with subsequent gel fluorography demonstrated that mean velocities (Vmean) of actin and β-tubulin, i.e. slow component b (SCb) transport in untreated diabetic rats were significantly lower than those in control rats (p<0.05, respectively); mean diameter of axons in the former rats was significantly smaller than that in the latter (p<0.01). Vmean of actin transport in GBe-treated diabetic rats was significantly faster than that in untreated diabetic rats (p<0.05). Vmean of slow axonal transport was significantly correlated with mean diameter of axons in the three groups of rats combined (p<0.01). On electron microscopy, severe altered endoneurial microvessels decreasing in luminal area together with endothelial cell degeneration or hypertrophy, pericyte debris and basement membrane thickening were observed in untreated diabetic rats; on the other hand these findings were less prominent in the diabetic rats treated with GBe. It is suggested that GBe treatment may protect disturbed slow axonal transport and pathological alterations of peripheral nerve with abnormal endoneurial microvasculature from diabetes mellitus by antioxidant activity