Glyphosate in fisheries management

Glyphosate is the active ingredient of the broad-spectrum, translocated herbicide Roundup. Glyphosate is cleared for safe use in or near watercourses, being rated virtually non-toxic by the World Health Organisation. Trials in and alongside Irish fishery watercourses first commenced in 1989 and are continuing to date. The aim of this work is to evaluate the product's efficacy in clearing nuisance reed species in recreational fisheries. The longevity of control and impact on the habitat and its fauna is also investigated. Trials in canal fisheries have demonstrated the capacity of glyphosate to remove obstructive stands of reeds (mainly Schoenoplectus lacustris, Glyceria maxima, Phragmites australis, Sparganium erectum and Typha latifolia), so creating reed-free areas and swims for anglers. These swims remained open for three years following a single application. In 1992 a trial over a 3 km length of the River Boyne, a renowned salmonid fishery, was undertaken. The results clearly demonstrated the ability of glyphosate to provide long-term control of dense (354 shoots m^–2) Schoenoplectus infestations in a large watercourse. In the year following, less than one shoot per m² was present in the channel. In 1994 a small increase in density (7.6 shoots m^–2 was recorded, so enabling unobstructed angling in a stretch of river that had been virtually unfishable for years. Trout (Salmo trutta L.) and salmon (Salmo salar L.) also used the newly exposed gravels for spawning in the winter of 1993, thereby improving fish recruitment and production in the fishery.     

Tidal marsh plant responses to elevated CO2, nitrogen fertilization,and sea level rise

Elevated CO₂ and nitrogen (N) addition directly affect plant productivity and the mechanisms that allow tidal marshes to maintain a constant elevation relative to sea level, but it remains unknown how these global change drivers modify marsh plant response to sea level rise. Here we manipulated factorial combinations of CO₂ concentration (two levels), N availability (two levels) and relative sea level (six levels) using in situ mesocosms containing a tidal marsh community composed of a sedge, Schoenoplectus americanus, and a grass, Spartina patens. Our objective is to determine, if elevated CO₂ and N alter the growth and persistence of these plants in coastal ecosystems facing rising sea levels. After two growing seasons, we found that N addition enhanced plant growth particularly at sea levels where plants were most stressed by flooding (114% stimulation in the + 10 cm treatment), and N effects were generally larger in combination with elevated CO₂ (288% stimulation). N fertilization shifted the optimal productivity of S. patens to a higher sea level, but did not confer S. patens an enhanced ability to tolerate sea level rise. S. americanus responded strongly to N only in the higher sea level treatments that excluded S. patens. Interestingly, addition of N, which has been suggested to accelerate marsh loss, may afford some marsh plants, such as the widespread sedge, S. americanus, the enhanced ability to tolerate inundation. However, if chronic N pollution reduces the availability of propagules of S. americanus or other flood‐tolerant species on the landscape scale, this shift in species dominance could render tidal marshes more susceptible to marsh collapse.     

Water column oxygen demand and sediment oxygen flux: patterns of oxygen depletion in tidal creeks

Low dissolved oxygen (DO) levels often occur during summer in tidal creeks along the southeastern coast of the USA. We analyzed rates of oxygen loss as water-column biochemical oxygen demand (BOD₅) and sediment oxygen flux (SOF) at selected tidal creek sites monthly over a 1-year period. Ancillary physical, chemical and biological data were collected to identify factors related to oxygen loss. BOD₅ rates ranged from 0.0 mg l^?1 to 7.6 mg l^?1 and were correlated positively with organic suspended solids, total suspended solids, chlorophyll a concentrations, temperature, and dissolved oxygen, and negatively with pH and nitrate + nitrite. SOF rates ranged from 0.0 to 9.3 g O₂ m^?2 d^?1, and were positively correlated with temperature, chlorophyll a, and total suspended solids, but negatively with dissolved oxygen. Both forms of oxygen uptake were seasonally dependent, with BOD₅ elevated in spring and summer and SOF elevated in summer and fall. Average oxygen loss to sediments was greater and more variable than oxygen loss in the water column. Oxygen deficits at three of five locations were significantly related to BOD₅ and SOF, but not at two sites where ground water discharges were observed. Correlation and principal component analyses suggested that BOD₅ and SOF responded to somewhat different suites of environmental variables. BOD₅ was driven by a set of parameters linked to warm season storm water inputs that stimulated organic seston loads, especially chlorophyll a, while SOF behaved less strongly so. Runoff processes that increase loads of organic material and nutrients and ground water discharges low in dissolved oxygen contribute to occurrences of low dissolved oxygen in tidal creeks.     

Can community structure track sea‐level rise? Stress and competitive controls in tidal wetlands

Climate change impacts, such as accelerated sea‐level rise, will affect stress gradients, yet impacts on competition/stress tolerance trade‐offs and shifts in distributions are unclear. Ecosystems with strong stress gradients, such as estuaries, allow for space‐for‐time substitutions of stress factors and can give insight into future climate‐related shifts in both resource and nonresource stresses. We tested the stress gradient hypothesis and examined the effect of increased inundation stress and biotic interactions on growth and survival of two congeneric wetland sedges, Schoenoplectus acutus and Schoenoplectus americanus. We simulated sea‐level rise across existing marsh elevations and those not currently found to reflect potential future sea‐level rise conditions in two tidal wetlands differing in salinity. Plants were grown individually and together at five tidal elevations, the lowest simulating an 80‐cm increase in sea level, and harvested to assess differences in biomass after one growing season. Inundation time, salinity, sulfides, and redox potential were measured concurrently. As predicted, increasing inundation reduced biomass of the species commonly found at higher marsh elevations, with little effect on the species found along channel margins. The presence of neighbors reduced total biomass of both species, particularly at the highest elevation; facilitation did not occur at any elevation. Contrary to predictions, we documented the competitive superiority of the stress tolerator under increased inundation, which was not predicted by the stress gradient hypothesis. Multifactor manipulation experiments addressing plant response to accelerated climate change are integral to creating a more realistic, valuable, and needed assessment of potential ecosystem response. Our results point to the important and unpredicted synergies between physical stressors, which are predicted to increase in intensity with climate change, and competitive forces on biomass as stresses increase.     

Characterization of microsatellite loci in Schoenoplectus americanus (Cyperaceae)

Schoenoplectus americanus is a model organism for studying ecological and ecosystem responses of salt marsh plant communities to global climate change. Here we characterize 16 microsatellite loci in S. americanus to facilitate studies on the genetic basis of phenotypic responses to changing climate conditions such as elevated atmospheric carbon dioxide. Most loci also amplified in the morphologically similar sister species, Schoenoplectus pungens. Five loci exhibited species‐specific alleles or distinct allelic size distributions that discriminate S. americanus from S. pungens.     

中国新记录穗芽水葱的分类学研究

该文报道了发现于浙江省景宁畲族自治县山地沼泽中的莎草科水葱属一中国新记录种———穗芽水葱(Schoenoplectus gemmifer C. Sato, T. Maeda ＆ Uchino)。该种外形与水毛花相似,但其秆质地较柔软,小穗较短,花柱2,具无性繁殖的穗芽。染色体数目为2n ＝78±2(水毛花的染色体数目为2n ＝44)。文献记载穗芽水葱特产于日本,并被列为日本稀有物种。该种在景宁的发现,对研究中国—日本植物区系具有重要学术价值。     

Phytoremediation of two types of sediment contaminated with Zn by Schoenoplectus americanus

The effect of different sediments on growth, Zn uptake, Zn plant distribution, and morphometric variables of Schoenoplectus americanus were investigated under controlled conditions. Two types of sediments were assayed: from a large natural levee (LS) and alluvial sediments (AS), the former with lower organic matter (OM) and nutrients content than AS, without and with added Zn (2500 microg Zn/g air-dry sediment). Zinc partition in sediment was determined. Increases in water conductivity and Zn concentrations in water and sediments were observed in artificially contaminated treatments. Plants showed a lower above ground growth rate, height, and width of shoots, and a higher Zn concentration in shoots and rhizomes. In the contaminated treatments, AS treatment showed lower Zn concentration in water and higher Zn concentration in sediments (total, exchangeable, and OM fractions) than LS treatment, due to Zn displacement from floodwater to sediments. The presence of a high level of OM and nutrients also increased aboveground biomass growth, whereas it decreased Zn concentration in shoots. Although the translocation factor increased with Zn addition, it was lower in AS treatment Sediments of AS treatments are a suitable environment for growth of S. americanus, which partially compensates the toxic effects of Zn. Our results provide an encouraging basis for planning larger scale experiments to test the role of OM and nutrients in improving phytoremediation.     

Small‐stature emergent macrophytes and crepuscular sprinkler disturbance reduce mosquito abundance in wetland mesocosms

The impact of emergent macrophyte species and crepuscular sprinkler disturbance on mosquito abundance over a 2‐year period was measured in wetland mesocosms. Mosquito oviposition and abundance of immature mosquitoes and aquatic invertebrates were monitored in monotypic plots of small‐stature (height of mature stands <1.5 m) alkali bulrush (Schoenoplectus maritimus) and large‐stature (height of mature stands > 2 m) California bulrush (Schoenoplectus californicus) without or with daily sprinkler showers to deter mosquito egg laying. Relative to wetlands without operational sprinklers, oviposition by culicine mosquitoes was reduced by > 99% and immature mosquito abundance was reduced by > 90% by crepuscular sprinkler applications. Mosquito abundance or distribution in wetlands did not differ between the two bulrush species subjected to the sprinkler treatment. Alkali bulrush wetlands without daily sprinkler treatments contained more egg rafts but significantly fewer mosquito larvae than did California bulrush wetlands. Predaceous damselfly naiads were 3–5 times more abundant in alkali bulrush than in California bulrush. Stem density, rate of spread, and autumnal mortality of alkali bulrush were higher than for California bulrush. Replacement of large emergent macrophytes by smaller species may enhance the efficacy of integrated mosquito management programs to reduce mosquito‐transmitted disease cycles associated with multipurpose constructed wetlands used worldwide for water reclamation and habitat restoration.     

An invasive wetland grass primes deep soil carbon pools

Understanding the processes that control deep soil carbon (C) dynamics and accumulation is of key importance, given the relevance of soil organic matter (SOM) as a vast C pool and climate change buffer. Methodological constraints of measuring SOM decomposition in the field prevent the addressing of real‐time rhizosphere effects that regulate nutrient cycling and SOM decomposition. An invasive lineage of Phragmites australis roots deeper than native vegetation (Schoenoplectus americanus and Spartina patens) in coastal marshes of North America and has potential to dramatically alter C cycling and accumulation in these ecosystems. To evaluate the effect of deep rooting on SOM decomposition we designed a mesocosm experiment that differentiates between plant‐derived, surface SOM‐derived (0–40 cm, active root zone of native marsh vegetation), and deep SOM‐derived mineralization (40–80 cm, below active root zone of native vegetation). We found invasive P. australis allocated the highest proportion of roots in deeper soils, differing significantly from the native vegetation in root : shoot ratio and belowground biomass allocation. About half of the CO₂ produced came from plant tissue mineralization in invasive and native communities; the rest of the CO₂ was produced from SOM mineralization (priming). Under P. australis, 35% of the CO₂ was produced from deep SOM priming and 9% from surface SOM. In the native community, 9% was produced from deep SOM priming and 44% from surface SOM. SOM priming in the native community was proportional to belowground biomass, while P. australis showed much higher priming with less belowground biomass. If P. australis deep rooting favors the decomposition of deep‐buried SOM accumulated under native vegetation, P. australis invasion into a wetland could fundamentally change SOM dynamics and lead to the loss of the C pool that was previously sequestered at depth under the native vegetation, thereby altering the function of a wetland as a long‐term C sink.     

Temporary drought can selectively suppress Schoenoplectus mucronatus in rice

Outdoor pot experiments were conducted in California to quantify differences in rice and Schoenoplectus mucronatus susceptibility to drought and to identify morphological and physiological traits that would favor rice over S. mucronatus under drought. Plants were grown in flooded soil for approximately 5 weeks, and then subjected to different drought periods after which pots were re-flooded. Chlorophyll fluorescence assays revealed that rice and S. mucronatus Fv/Fm first became <0.8 after leaf water potential (Ψ_leaf) had decreased to approximately −4 MPa and −2 MPa, respectively. Thus, by suffering less photosynthetic damage from drought, rice had better recovery after re-flooding than S. mucronatus. When drought reduced Ψ_leaf to −3 MPa, S. mucronatus re-growth was nearly suppressed but that of rice was unaffected. Rice plants depleted soil moisture 1.6 faster than S. mucronatus due to larger and deeper roots and a high water-spending strategy (when Ψ_leaf decreased from approximately −0.5 MPa to −2.5 MPa, ¹³δ increased from −27.8 to −27.4 and from −28.1 to −26.0 for rice and S. mucronatus, respectively). Rice under interspecific competition sustained its Ψ_leaf by extracting more water from greater depths, while causing severe moisture stress and photosynthetic damage to S. mucronatus. Thus temporary drought enhanced rice competitiveness over S. mucronatus, supporting the concept of using brief drought as a tool for S. mucronatus suppression in rice. The Ψ_leaf developed by the end of the drought period predicted rice yields (R² = 0.77, P < 0.0001) and the capacity of S. mucronatus to recover from drought upon irrigation resumption (R² = 0.62, P < 0.001). Brief (8-10 d) drought imposed on 5-week-old rice did not significantly depress late-season rice biomass growth or grain yields, while S. mucronatus never fully recovered from drought. Rice yields were only reduced after Ψ_leaf reached values below approximately −2.5 MPa. Longer drought (∼20 d) delayed maturity and reduced rice yields by approximately 60-80%. The dry-down approach could help suppress weeds similar to S. mucronatus in organic rice where premium prices can compensate for lower grain yield.