Data collected as part of the International Biological Program from 43 lakes and 12 reservoirs, distributed from the tropics to the arctic, were subjected to statistical analysis to establish which factors are important in controlling production and how they are related. In the whole body of data, variables related to solar energy input have a greater influence on production than variables related to nutrient concentration; in lakes within a narrow range of latitude, nutrient-related variables assume greater importance. Morphological factors have little influence on productivity per unit area in either case. Chlorophyll a concentration is a good indicator of nutrient conditions and when combined with an energyrelated variable constitutes a good estimator of primary production.

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Four experimental trawls were made at highwater over the intertidal zone of the Minas Basin and the effects assessed when the tide was out to determine the physical and biological impacts of groundfish trawling on the benthos. The trawl doors made furrows 30–85 cm wide and up to 5 cm deep. The rollers compressed surficial sediments but did not scour a depression. The bridle caused no obvious disturbance. Door furrows and roller marks remained visible for 2–7 mo. No significant impacts were observed on either benthic diatoms or macrobenthos. The macrobenthos was dominated by polychaetes, some of which may have the ability to take evasive action as a trawl approaches. There were few molluscs, crustaceans, or echinoderms present; these taxa have been shown to be more susceptible to trawling damage in studies done elsewhere. Nematode numbers were initially depressed in the door furrows but did recover with time. It is not known whether nematodes were killed or displaced but the latter is thought more likely. Overall, the impacts in this particular environment are judged to be minor, especially since the intertidal sediments of the Minas Basin are already exposed to similar natural stresses imposed by storms and winter ice.

The stability of a mudflat in the Humber estuary, South Yorkshire, was investigated at seven sites along a shore-normal transect during early spring. This was carried out using the benthic flume Sea Carousel, and from the investigation of surface samples in a laboratory equivalent to the Sea Carousel, the Lab Carousel. A clear trend in erosion threshold [%(0)] was evident, showing two maxima: the greatest on the inner mudflat (0.78 Pa); and a second on the central mudflat (0.75Pa). We ascribe these maxima to two causes: (1) desiccation of the inner mudflats; and (2) biostabilization by algae of the central flats. Our results suggest that of these factors biostabilization was the dominant one at the time of the study. Most of the variation in erosion rate is explained through the sediment bulk density (Pb) and colloidal carbohydrate (DCHO): [To(0)] = 0.511.931og10(DCHO + 2.5 × 10-4pb] q-1.7; r 2 = 0.63. Thus variations in DCHO had O(104) greater impact on erosion threshold than equivalent variations Pb. The relationship between mean erosion rate (Era) and current speed (Uy) was similar for all sites and is defined by the exponential function: Em = 2.47 × 10 -6 • 10(3-749uy) kgm -2 s -1 . In situ mean still-water settling rates (Ws) were up to 2.46 × 10-3m s -l, which is up to an order of magnitude faster than was measured in other estuaries at similar suspended sediment concentrations, S. The decay constant, k, for still-water settling appeared to be a linear function of S, and compared favourably with values derived from five Canadian coastal mudflats. Results from Lab Carousel showed that the erosion thresholds were the same as those measured in situ, using Sea Carousel. Furthermore the spatial trends in erosion were at University of Chicago on July 24, 2015 http://sp.lyellcollection.org/ Downloaded from 26 C. L. AMOS ET AL.