Isidro Bosch

The Impact of Agricultural Best Management Practices on Downstream Systems: Soil Loss and Nutrient Chemistry and Flux to Conesus Lake, New York, USA

ABSTRACT Six small, predominantly agricultural (>70%) watersheds in the Conesus Lake catchment of New York State, USA, were selected to test the impact of Best Management Practices (BMPs) on mitigation of nonpoint nutrient sources and soil loss from farms to downstream aquatic systems. Over a 5-year period, intensive stream water monitoring and analysis of covariance provided estimates of marginal means of concentration and loading for each year weighted by covariate discharge. Significant reductions in total phosphorus, soluble reactive phosphorus, nitrate, total Kjeldahl nitrogen, and total suspended solids concentration and flux occurred by the second year and third year of implementation. At Graywood Gully, where Whole Farm Planning was practiced and a myriad of structural and cultural BMPs were introduced, we observed the greatest percent reduction (average = 55.8%) and the largest number of significant reductions in analytes (4 out of 5). Both structural and cultural BMPs were observed to have profound effects on nutrient and soil losses. Where fields were left fallow or planted in a vegetative type crop, reductions, especially in nitrate, were observed. Where structural implementation occurred, reductions in total fractions were particularly evident. Where both were applied, major reductions in nutrients and soil occurred. After 5 years of management, nonevent and event concentrations of total suspended solids in streams draining agricultural watersheds were not significantly different from those in a relatively “pristine/reference” watershed. This was not the case for nutrients.

Influence of Ozone-Related Increases in Ultraviolet Radiation on Antarctic Marine Organisms1

SYNOPSIS. Every spring for the past two decades, depletion of stratospheric ozone has caused increases in ultraviolet B radiation (UVB, 280–320 nm) reaching Antarctic terrestrial and aquatic habitats. Research efforts to evaluate the impact of this phenomenon have focused on phytoplankton under the assumption that ecosystem effects will most likely originate through reductions in primary productivity; however, phytoplankton do not represent the only significant component in ecosystem response to elevated UVB. Antarctic bacterioplankton are adversely affected by UVB exposure; and invertebrates and fish, particularly early developmental stages that reside in the plankton, are sensitive to UVB. There is little information available on UV responses of larger Antarctic marine animals (e.g., birds, seals and whales). Understanding the balance between direct biological damage and species-specific potentials for UV tolerance (protection and recovery) relative to trophic dynamics and biogeochemical cycling is a crucial factor in evaluating the overall impact of ozone depletion. After more than a decade of research, much information has been gathered about UV-photobiology in Antarctica; however, a definitive quantitative assessment of the effect of ozone depletion on the Antarctic ecosystem still eludes us. It is only obvious that ozone depletion has not had a catastrophic effect in the Antarctic region. The long-term consequences of possible subtle shifts in species composition and trophic interactions are still uncertain.

Photoperiodic regulation of gametogenesis in the Antarctic sea star Odontaster validus Koehler: Evidence for a circannual rhythm modulated by light

Summary The common Antarctic sea star Odontaster validus spawns in mid-winter, following a long period of gametogenesis. In a 2-year experiment at McMurdo Sound where sea temperature remains at freezing year round, we found that gametogenesis in sea stars kept on photoperiods 6 months out of phase with ambient (constant light in winter, constant dark in summer) had, within a year, switched to 6 months out of phase with stars kept on an ambient photoperiod or collected from the field. Gametogenesis in sea stars kept in constant light or on a 12 h light: 12 h dark photoperiod appeared to be maintained more or less continuously; photoperiods of 12 h or more apparently stimulate gametogenesis. In contrast, gametogenesis in sea stars kept in constant darkness was the same as in sea stars kept on an ambient photoperiod or collected from the field, indicative of an underlying circannual rhythm similar to that known for the NE Pacific sea star Pisaster ochraceus. Such a rhythm could maintain gametogenic synchrony among different populations with different light regimes, including those in deeper water where light is very dim or absent. If so, the rhythm would need to be set in larvae when they are near the sea surface in the summer.

Management of Agricultural Practices Results in Declines of Filamentous Algae in the Lake Littoral

ABSTRACT Filamentous algal cover was quantified during periods of peak biomass from 2001 to 2007 in six littoral macrophyte beds in Conesus Lake, New York (USA). Three of the study sites were adjacent to streams that drained sub-watersheds where extensive agricultural best management practices (BMPs) designed to reduce nutrient runoff were implemented beginning in 2003. Three other study sites were downstream from sub-watersheds where only a few or no BMPs were implemented by landowners. For the sites that received extensive management, comparisons of the Pre-BMP baseline period (2–3 yrs) to the Post-BMP period (4 yrs) revealed that algal cover was statistically lower than baseline in eight of eleven years (72.7%). For the three sites where limited or no management was implemented, the percent cover of filamentous algae was lower than Pre-BMP baseline levels in only three of twelve years (25%). Where major reductions in cover of filamentous algae occurred, positive relationships existed with summer stream loading of nitrate and soluble reactive phosphorus to the nearshore. In some cases only nitrate loading was significantly correlated with percent cover, indicating that the relative importance of nitrogen and phosphorus to algal growth near streams may be determined by the characteristics and land use within each sub-watershed. Agricultural BMPs targeting nutrient and suspended solid runoff can effectively reduce filamentous algal growth locally along the lake littoral zone on a time scale of months to a few years and with moderate commitment of resources. This work offers a new perspective for management of the growing problem of littoral algal growth in the embayments and drowned river mouths of the Great Lakes.

Elevated Nutrient Levels from Agriculturally Dominated Watersheds Stimulate Metaphyton Growth

ABSTRACT The linkage between land use in a catchment basin and downstream aquatic ecosystems, especially effects on algae attached to substrata or loosely aggregated in the littoral zone, represents a void in our understanding of lake systems. The occurrence of beds of metaphyton at some stream mouths and not others in Conesus Lake, NY (USA) provided an opportunity to consider the relationship between land use and phosphorus and nitrogen losses on the development of shoreline metaphyton blooms. Experiments were performed in the littoral zone of a large temperate lake to test the hypothesis that effluent high in phosphorus and nitrate from tributaries draining agricultural watersheds had a stimulatory effect on the growth of littoral metaphyton, while effluent from a forested watershed did not. The study encompassed six watersheds of varying agricultural use (60–80%) and a forested watershed (12% agriculture). For each experiment, two quadruplicate sets of plexiglass incubation chambers (height = 50 cm, interior diameter = 9.5 cm) containing native assemblages of metaphyton received lake or tributary water continuously over a 3-day lake incubation period. Growth of metaphyton incubated in lake water and in tributary water was compared and differences appeared to be related to nutrient concentrations. A statistically significant stimulatory effect was measured for the six tributaries draining agricultural watersheds but not for the forested watershed. Tributary loadings appear to stimulate metaphyton at sites where the hydrology and hydrodynamincs are suitable. A significant positive linear relationship existed between percent metaphyton cover in the littoral zone and the percent of land use in agriculture. Metaphyton abundance is impacted by land use practices and subsequent loss of nutrients from the catchment.

Mating behavior of a brooding Antarctic asteroid, Neosmilaster georgianus

Summary Spawning behavior and male-female superposition of Neosmilaster georgianus, a common brooding asteroid, were observed both in the field and the laboratory at Palmer Station, Antarctica, during the austral spring of 1991. Pseudocopulation is preceded by exploration, contact, and mounting of a female by individual or multiple males. Male pre-mating activity in the field was initiated by the spawning of a nearby conspecific female. However, in laboratory experiments a similar pattern of activity was triggered by the presence of spawning conspecific males or male sea urchins, indicating the presumed inductive signal lacks specificity. Pseudocopulation in this species may ensure maximal fertilization and enhance reproductive success. This is the first reported instance of aggregative spawning in an Antarctic echinoderm. Moreover, pseudocopulation is a rare phenomenon among echinoderms worldwide and N. georgianus is only the third asteroid described to utilize this fertilization strategy.

The impact of stream nutrient loading on macrophytes and metaphyton in Conesus Lake, USA

During the summers of 2000, 2001 and 2002, the littoral zone of Conesus Lake (40°54 N, 77°43 W) supported massive blooms of metaphyton, mostly filamentous green algae (Zygnema sp. and Spirogyra sp.). Extensive agricultural activity (60–80% of the land use) within the lake’s western subwatersheds is responsible for the loading of large quantities of nitrate (up to 1800 g/ha/day) and total phosphorus (up to 34 g/ha/day) into the lake during precipitation events (MAKAREWICZ et al. 2001). Large assemblages of M. spicatum and accompanying metaphyton growth were often located near stream mouths (Fig.1) and a significant correlation existed between stream nutrient loading (total phosphorus, soluble reactive phosphorus and nitrate nitrogen) during precipitation events and the standing crop of macrophytes (Fig.2). To further evaluate the relationship between stream nutrient loading and growth of metaphyton, the hypothesis that stream effluent high in dissolved phosphorus and nitrate had a stimulatory effect on Conesus Lake metaphyton biomass was tested in situ in continuous flow incubation chambers.

Responses of lake macrophyte beds dominated by Eurasian watermilfoil (Myriophyllum spicatum) to best management practices in agricultural sub-watersheds: Declines in biomass but not species dominance

ABSTRACT Long-term studies of macrophyte beds growing near streams in Conesus Lake, New York, have revealed a high biomass and continuing dominance of the invasive rooted species Eurasian watermilfoil (Myriophyllum spicatum). We tested whether agricultural best management practices (BMPs) designed to reduce tributary nutrient and soil loss from the watershed could reduce populations of Eurasian watermilfoil downstream in the lake littoral. Six macrophyte beds were monitored during a 3-year baseline period (2001–2003) prior to the implementation of BMPs and for a 4-year experimental period after a variety of agricultural BMPs were implemented in three sub-watersheds. For three macrophyte beds downstream from sub-watersheds managed as part of our project, quadrat biomass decreased by 30–50% and was statistically lower than Pre-BMP baseline values in 7 of 11 experimental sample years. Biomass loss primarily in the form of the dominant Eurasian watermilfoil ranged from 6.2 to 10 t wet weight for each bed. The declines in biomass coincided with significant annual and January—August decreases in the concentrations and fluxes of dissolved nutrients, total phosphorus, and total suspended solids in nearby streams. For three macrophyte beds downstream from watersheds in which landowners applied less extensive or no new agricultural management, biomass was statistically indistinguishable from Pre-BMP baseline values in all 12 experimental sample years. Milfoil remained the overwhelmingly dominant species at all sites during the entire study period. These results provide impetus for the use of watershed nutrient management to control the nuisance growth of Eurasian Watermilfoil on a local scale in the lake littoral.

In situ experimental studies of Eurasian Watermilfoil (Myriophyllum spicatum) downstream from agricultural watersheds: Nutrient loading, foliar uptake, and growth

ABSTRACT Recent studies in Conesus Lake, New York, documented significant decreases in the biomass of Eurasian watermilfoil (Myriophyllum spicatum) near the mouths of streams draining sub-watersheds where reductions in nutrient loading occurred as a result of the implementation of agricultural Best Management Practices (BMPs). In situ experiments were conducted to further investigate the relationship between stream loading, foliar uptake, and growth of Eurasian watermilfoil. In two of three experiments, plants cropped to a height of approximately 50 cm had the lowest growth (g/m2) downstream from a sub-watershed where major BMPs had been implemented (80% and 0%). In sub-watersheds where minimal or no BMPs were introduced, plants showed significantly higher growth as biomass increased (216% and 22%). In a second set of experiments, shoots of Eurasian watermilfoil plants were incubated for 24 h in ambient lake water and in lake water with enriched concentrations of nitrate and soluble reactive phosphorus comparable to rain event stream effluent concentrations and then allowed to grow in situ for a 2-week experimental period. For all experiments combined, the shoot biomass increased significantly in the enhanced nutrient treatments when compared to the ambient treatment at the Sand Point macrophyte bed (reduced loading) but not at the Eagle Point macrophyte bed (high loading). Overall, the results indicate that foliar uptake of nutrients in stream effluent can contribute to the growth of Eurasian watermilfoil and reinforce the hypothesis that reductions in stream loading through agricultural BMPs can help reduce macrophyte growth in the lake littoral.