The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations

Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, KD. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in KD were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the KD (n = 15 for each metal, p > 0.05) for Mn (r2 = 0.0063), Cu (r2 = 0.0002, Cr (r2 = 0.021), Ni (r2 = 0.0023), Cd (r2 = 0.00001), Co (r2 = 0.096), Hg (r2 = 0.116) or Pb (r2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of KD. The findings conform to the increasingly documented theory that the use of KD in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 μg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water

A method to choose water depths for zooplankton samples in lakes

Publication history: Accepted - 13 October 2021; Published online - 23 November 2021.As methods in the literature to sample zooplankton in lakes mostly offered general guidance on the sample depths, a new one was developed. Using the principle of volume-weighted sampling of the lake volume and an empirical function for the hypsometric curve, formulae for the volumes and areas of five equal sections of the lake were derived, which were then used to calculate section mean depths. Vertical net hauls taken at the mean depths are combined using a relation between their mean depths to produce one unbiased composite sample of the zooplankton. While generic formulae were derived, starting values for the depths that divide the lake volume into five equal sections are needed in order to apply the method, which then optimizes the depths; the method is implemented in a spreadsheet. The method was applied to four hypothetical lakes of maximum depth 12 m that cover a wide variation of lake form and how the sample depths vary with form was described; as lake form becomes more convex, the sample depths decrease, reflecting that more of the lake volume is at shallower depth. The method was used to estimate the whole-lake abundance of zooplankton in 51 lakes and no practical difficulties were encountered. It can be used in lakes up to a few tens of km2 in area.The INTERREG IVA Programme of the European Union’s European Regional Development Fund, managed by the Special European Union Programmes Body, funded this work. It formed part of the cross-border DOLMANT project (reference number 002862)

The Drought Monitor Comes of Age

The 20th century featured immense scientific discoveries and advances. Astrophysics gained Einstein’s life-altering theory of relativity, opening the door to nuclear weaponry and the mind-bending Big Bang theory. The medical field achieved stunning success in suppressing or vanquishing a host of deadly diseases, including polio and smallpox. And through advances in computing technology, meteorological forecasting moved from backof- the-envelope calculations to supercomputers. However, drought monitoring fell behind the curve of scientific advancement. Not until 1965, when the U.S. Department of Commerce published Wayne C. Palmer’s “Research Paper No. 45: Meteorological Drought,” was there even a complex mathematical definition of drought. In his foreword, Palmer explained that “meteorological science has not yet come to grips with drought. It has not even described the phenomenon adequately.” The Palmer Drought Severity Index (PDSI) was the earliest attempt to describe an imbalance between water supply and water demand, by integrating water supply (precipitation) and water demand (evapotranspiration, as computed from temperature) in a water-budget calculation that also included water storage in the soil. It also established an intensity scale for drought and identified when drought began and ended. Yet the PDSI was never really designed for national drought monitoring, as Palmer’s focus was on the Great Plains and the western Corn Belt; born in 1915, he grew up in south-central Nebraska, shaped by the 1930s Dust Bowl. Clearly, Palmer did not create the PDSI from thin air. He worked for years perfecting his equations, and many of his studies of U.S. droughts of the 1890s, 1910s, 1930s, and 1950s were published in the federal Weekly Weather and Crop Bulletin and other outlets, including the Monthly Weather Review and the Bulletin of the American Meteorological Society. Though not among six dozen references listed in “Research Paper No. 45,” “A Simple Index of Drought Conditions,” an article by James McQuigg of the U.S. Weather Bureau published in a 1954 issue (Volume 7, Issue 3) of Weatherwise might have influenced Palmer. Palmer’s 1965 work, as remarkable as it was for that time, was not the final word on drought. In 1968, three years after introducing the PDSI, he added the complementary Crop Moisture Index, recognizing that drought affects agriculture and hydrology on differing time scales—and at different soil depths

A preliminary classification of lake types in Northern Ireland

The EC Water Framework Directive (WFD) introduces the concept of theecological status of surface waters. In order to compare the ecologicalstatus of, for example, lakes across Europe, methods based on either theidea of the continuum or of discrete biological communities need to bedeveloped. The best example of the use of the continuum approach is thatof RIVPACS for macroinvertebrates in rivers (Wright et al. 1998, 2000),and for discrete communities that of Johnson & Goedkoop (2000) for lakemacroinvertebrates

Long-term changes in oxygen depletion in a small temperate lake: effects of climate change and eutrophication

1. We analysed 41 years of data (1968–2008) from Blelham Tarn, U.K., to determine the consequences of eutrophication and climate warming on hypolimnetic dissolved oxygen (DO). 2. The establishment of thermal stratification was strongly related to the onset of DO depletion in the lower hypolimnion. As a result of a progressively earlier onset of stratification and later overturn, the duration of stratification increased by 38 ± 8 days over the 41 years. 3. The observed rate of volumetric hypolimnetic oxygen depletion (VHODobs) ranged from 0.131 to 0.252 g O2 m−3 per day and decreased significantly over the study period, despite the increase in the mean chlorophyll a (Chl a) concentration in the growing season. The vertical transport of DO represented from 0 to 30% of VHODobs, while adjustments for interannual differences in hypolimnetic temperature were less important, ranging from −11 to 9% of VHODobs. 4. The mean wind speed during May made the strongest significant contribution to the variation in VHODobs. VHODobs adjusted for the vertical transport of DO and hypolimnetic temperature differences, VHODadj, was significantly related to the upper mixed layer Chl a concentration during spring. 5. Hypolimnetic anoxia (HA) ranged from 27 to 168 days per year and increased significantly over time, which undoubtedly had negative ecological consequences for the lake. 6. In similar small temperate lakes, the negative effects of eutrophication on hypolimnetic DO are likely to be exacerbated by changes in lake thermal structure brought about by a warming climate, which may undermine management efforts to alleviate the effects of anthropogenic eutrophication