Spatial patterns in fish biomass and relative trophic level abundance in a wastewater enriched river

Abstract –  It is generally accepted that nutrient enrichment of aquatic systems will lead to increased production at the top trophic level (fish). We found that in the wastewater enriched Bow River, Alberta rainbow trout ( Oncorhynchus mykiss ) biomass increased over 25-fold, and brown trout ( Salmo trutta ) biomass increased 5-fold, however total sportfish biomass did not increase below the nutrient input point source. This was due to a dramatic downstream decrease in mountain whitefish ( Prosopium williamsoni ) biomass to 2% of the average biomass upstream of the municipal effluent source. The spatial pattern over a 177-km river section encompassing the city of Calgary, showed that the increase in trout abundance approximately tracked the expected nutrient concentrations in the river, but with a downstream lag of 20–30 km. Mountain whitefish biomass over the 177 km was inversely related to the dominant trout species, rainbow trout. Invertebrate abundance, macrophyte biomass and phytoplankton biomass all increased below the wastewater treatment plant outfalls. However, periphyton data were highly variable and showed no response. We propose several hypotheses as regards the factors that may have led to the decrease in mountain whitefish, based on the data from all trophic levels and the spatial pattern for fish biomass. Proposed factors influencing the mountain whitefish decline were; altered competitive ability because of macrophyte abundance, ammonia toxicity and barriers to movement (weirs).     

The decline of the sand lizard, Lacerta agilis L. Population on the sand dunes of the Merseyside coast,England

The population of the sand lizard Lacerta agilis in northwest England has declined sharply since 1930. The reasons for this decline are considered.Between Southport and the River Alt, approximately 50% of the sand dune habitat has been destroyed and a further 12% modified since 1801. Habitat losses resulting from building developments help to explain the sand lizard decline. The species has also disappeared from areas still supporting dune habitat. Here a combination of factors appear responsible, the effects of which are not uniform throughout the dune system.It is concluded that, in conjunction with a trend of less favourable climate over the last 15 years, habitat destruction, fragmentation and change of quality have brought about a catastrophic decline in the sand lizard population within the last 20 years. It is predicted that this population will become extinct before 2000 unless present trends are halted and adequate conservation measures taken.     

The effects of clipping height and frequency on net primary production of Andropogon gerardii (C4 grass) and Bromus inermis (C3 grass) in greenhouse experiments

There are potential agronomic and environmental benefits from incorporating warm‐season (C₄) grasses into temperate pasture systems, usually dominated by cool‐season (C₃) grasses, but there is a lack of information on how frequency and height of defoliation affects C₄ grasses. Three greenhouse experiments were conducted under (i) spring, (ii) summer and (iii) spring + summer clipping regimes. In each experiment, the effects of clipping frequency (weekly and monthly) and clipping height (clipped to 5 and 10 cm) were determined on above‐ and below‐ground net primary production (ANPP and BNPP) and total and seasonal dry matter (DM) yield for Andropogon gerardii Vitman (big bluestem, C₄ grass) and Bromus inermis Leyss (smooth brome, C₃ grass). Six replicates per treatment were used. In all experiments, ANPP and BNPP of smooth brome was greater than that of big bluestem although during late summer months big bluestem had higher DM yields of herbage than smooth brome. There were different effects of frequency and height of clipping for both species on two similar measurements: total annual DM yield and ANPP, indicating that the ability to generalize about the effects of defoliation from ecological and agronomic grassland standpoints is questionable. Clipping effects on ANPP and BNPP were different for summer‐clipped pots than for spring, and spring + summer‐clipped pots, indicating that management could be tailored to meet specific agronomic or conservation goals.     

In this issue – December 2010

Aged horses in Queensland · Pressor therapy in neonatal foals · Fluoroscopic stents for feline urethral obstruction · Intradermal sodium lauryl sulfate as an alternative to mulesing in lambs · Monepantel faecal residues and dung fauna · Surgical spaying in yearling Brahman heifers · Anthelmintic resistance in cattle nematodes