Consumption Dynamics of the Adult Piscivorous Fish Community in Spirit Lake, Iowa

At Spirit Lake, one of Iowa’s most important fisheries, walleye Sander vitreus (formerly Stizostedion vitreum) is one of the most popular species with anglers. Despite a century of walleye stocking and management in Spirit Lake, walleye growth rate, size structure, and angler harvest continue to decline. Our purpose was to determine the magnitude and dynamics of walleye population consumption relative to those of other piscivorous species in Spirit Lake, which would allow managers to judge the feasibility of increasing the abundance, growth rate, and size structure of the walleye population.We quantified food consumption by the adult piscivorous fish community in Spirit Lake over a 3-year period. Data on population dynamics, diet, energy density, and water temperature from 1995 to 1997 were used in bioenergetics models to estimate total consumption by walleye, yellow perch Perca flavescens, smallmouth bass Micropterus dolomieu, largemouth bass Micropterus salmoides, black crappie Pomoxis nigromaculatus, and northern pike Esox lucius. Estimated annual consumption by the piscivorous community varied roughly fourfold, ranging from 154,752 kg in 1995 to 662,776 kg in 1997. Walleyes dominated total consumption, accounting for 68, 73, and 90% (1995–1997, respectively) of total food consumption. Walleyes were also the dominant consumers of fish, accounting for 76, 86, and 97% of piscivorous consumption; yellow perch followed, accounting for 16% of piscivorous consumption in 1995 and 12% in 1996. Yellow perch were the predominant fish prey species in all 3 years, accounting for 68, 52, and 36% of the total prey consumed. Natural reproduction is weak, so high walleye densities are maintained by intensive stocking. Walleye stocking drives piscivorous consumption in Spirit Lake, and yearly variation in the cannibalism of stocked walleye fry may be an important determinant of walleye year-class strength and angler success. Reducing walleye stocking intensity, varying stocking intensity from year to year, and attempting to match stocking intensity with the abundance of prey species other than walleye may improve the walleye fishery in Spirit Lake

Metal–Ligand Cooperativity Promotes Reversible Capture of Dilute CO₂ as a Zn(II)-Methylcarbonate

In this study, a series of thiosemicarbazonato–hydrazinatopyridine metal complexes were evaluated as CO2 capture agents. The complexes incorporate a non-coordinating, basic hydrazinatopyridine nitrogen in close proximity to a Lewis acidic metal ion allowing for metal–ligand cooperativity. The coordination of various metal ions with (diacetyl-2-(4-methyl-thiosemicarbazone)-3-(2-hydrazinopyridine) (H2L1) yielded ML1 (M = Ni(II), Pd(II)), ML1(CH3OH) (M = Cu(II), Zn(II)), and [ML1(PPh3)2]BF4 (M = Co(III)) complexes. The ML1(CH3OH) complexes reversibly capture CO2 with equilibrium constants of 88 ± 9 and 6900 ± 180 for Cu(II) and Zn(II), respectively. Ligand effects were evaluated with Zn(II) through variation of the 4-methyl-thiosemicarbazone with 4-ethyl (H2L2), 4-phenethyl (H2L3), and 4-benzyl (H2L4) derivatives. The equilibrium constant for CO2 capture increased to 11,700 ± 300, 15,000 ± 400, and 35,000 ± 200 for ZnL2(MeOH), ZnL3(MeOH), and ZnL4(MeOH), respectively. Quantification of ligand basicity and metal ion Lewis acidity shows that changes in CO2 capture affinity are largely associated with ligand basicity upon substitution of Cu(II) with Zn(II), while variation of the thiosemicarbazone ligand enhances CO2 affinity by tuning the metal ion Lewis acidity. Overall, the Zn(II) complexes effectively capture CO2 from dilute sources with up to 90%, 86%, and 65% CO2 capture efficiency from 400, 1000, and 2500 ppm CO2 streams