Episodic struvite deposits in a Northern Great Plains flyway lake: indicators of mid-Holocene drought?

Abstract

A series of 34 layers of struvite (hydrous Mg-ammonium-phosphate) were deposited in laminated sediments of Kettle Lake, North Dakota, in the Northern Great Plains, USA. Sedimentologic, mineralogic and nitrogen isotopic evidence suggest that struvite was deposited during nutrient-enriched eutrophication events within a Mg-rich lacustrine environment. The struvite layers are dispersed between 4650 and 8700 cal. yr BP, with particularly high frequency between 8068 and 8700 cal. yr BP. The youngest struvite layer dates to 2734 cal. yr BP. Key features of the struvite-forming events were (a) relatively low water stage and consequent elevated water salinity associated with the dry mid Holocene, (b) disappearance of most lakes and wetlands in the region, and (c) focused, but brief, visitations by large populations of migratory waterfowl. The lack of more frequent occurrence of struvite is ascribed to the rarity with which this combination of conditions was achieved, in combination with difficulty of preservation for this salt. 15N isotopes in struvite (mean 7.51‰) are heavy relative to 15N in sediment and also extremely uniform over time. The isotopes are interpreted to reflect a waterfowl waste source without extensive NH4 volatilizaton. The timing of the struvite events does not closely correspond to century-scale mid-Holocene drought cycles inferred from oscillating aragonite concentrations, although there is a weak preferred occurrence in the humid phase of these cycles. Thus the struvite events are ephemeral prairie features of this generally arid period but tend not to occur at precisely the most arid intervals.

Environmental history of a closed-basin lake in the US Great Plains: Diatom response to variations in groundwater flow regimes over the last 8500 cal. yr BP

“…The relatively high permeability of the surrounding substratum gives the lake a strong connection with groundwater, and Kettle Lake is a flowthrough groundwaterdominated lake. Indeed, the chemistry of the lake is not significantly different from the relatively fresh groundwater (1.2 g/l) of the Little Muddy Aquifer (Donovan and Grimm, 2007). Because of this strong connection with ground water, the salinity of Kettle Lake (0.8 g/l) is somewhat anoma lous in a region where lakewater chemistries are strongly driven by evaporative losses (Last, 1993).…”

“…The two cores were aligned strati graphically and a composite continuous sedimentary sequence 21.87 m in length was developed (Donovan and Grimm, 2007;Grimm et al, 2011). While laminations are present throughout the core, they are not consistently annual and cannot be used for varve chronology.…”

“…While laminations are present throughout the core, they are not consistently annual and cannot be used for varve chronology. However, their presence is representative of anoxic bottom waters in Kettle Lake, at least for part of the year, and an alternating seasonal sedimentation of dark organic and detrital clastic layers with light aragonite layers (Donovan and Grimm, 2007).…”

Post-depositional formation of vivianite-type minerals alters sediment phosphorus records

“…9). Struvite is observed in freshwater sediments (Cohen and Ribbe, 1966;Donovan and Grimm, 2007;Pi et al, 2010), and porewater saturation calculations indicate that struvite might also be present in some brackish-marine systems (e.g., Kau Bay and Saanich Inlet; Middelburg, 1990;Murray et al, 1978). In order for struvite to precipitate, porewaters need to be elevated in NH + 4 and PO 4 and have high molar Mg / Ca porewater ratios (e.g., above 580 mol mol −1 by pH 7.6-7.9 and a PO 4 concentration of 10 µM; Gull and Pasek, 2013), conditions that are not met in the Bornholm Basin (Fig.…”

Identifying sediment discontinuities and solving dating puzzles using monitoring and palaeolimnological records

“…In turn, information on sedimentation processes may allow for inferences of key environment changes in the past, e.g. floods, earthquakes, fire, or human reclamation events (Arnaud et al, 2002;Moreno et al, 2008) and although sediment disturbances can be disadvantageous, numerous palaeolimnological studies have revealed that a reasonable chronology can be achieved, especially where multicore comparisons allow sediment disturbances to be distinguished (Tibby 2001;Donovan and Grimm, 2007;Morellón et al, 2011).…”