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Groundwater-wetland ecosystem interaction in the semiarid glaciated plains of North America

Interaction des écosystèmes eau souterraine-zone humide sur une plaine glaciaire semi-aride d’Amérique du Nord

Interacción el agua subterránea y el ecosistema de un humedad en la llanura glacial semiárida de Norteamérica

Interacção águas subterrâneas-ecossistemas húmidos em planícies geladas semi-áridas da América do Norte

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Abstract

The prairie wetlands of northern USA and Canada exist in numerous topographical depressions within the glaciated landscape. The wetlands are disconnected from each other most of the time with respect to surface-water drainage. The wetland water balance is controlled by snowmelt runoff and snowdrift from the surrounding uplands, precipitation, evapotranspiration, groundwater exchange, and occasional “fill-spill” connections to other wetlands. Salinity of water and the seasonal variability of water level in these wetlands have a strong influence on the ecosystem. Clay-rich glacial tills, covering much of the region, have very low (0.001–0.01 m/yr) hydraulic conductivity, except for the top several meters where the factures and macropores increase conductivity up to 1,000 m/yr. Transpiration in the wetland margin induces infiltration and lateral flow of shallow groundwater from wetland ponds through the high-conductivity zone, which strongly affects the water balance of wetlands. In contrast, groundwater flow in the deeper low-conductivity till has minor effects on water balance, but has a strong influence on salinity because the flow direction determines if the salts accumulate in wetlands (upward flow) or are leached out (downward flow) under wetlands. Understanding of the roles of shallow and deep groundwater systems will improve the hydrological conceptual framework for the management of wetland ecosystems.

Résumé

Des prairies de zones humides du Nord des Etats-Unis et du Canada existent dans de nombreuses dépressions de morphologie glaciaire. Du point de vu réseau de drainage, les zones humides sont la plupart du temps déconnectées entre elles. Le bilan en eau des zones humides est contrôlé par le ruissellement de la neige fondue et des congères des collines avoisinantes, les précipitations, l’évapotranspiration, l’échange avec les eaux souterraines, et des connexions occasionnelles de type “fill-spill” vers d’autres zones humides. La salinité des eaux et la variabilité saisonnière des niveaux d’eau dans ces zones humides ont une forte influence sur les écosystèmes. Les moraines glacières riches en argiles recouvrant une grande partie de la région ont des conductivités hydrauliques très faibles (0.001–0.01 m/an) sauf pour les quelques derniers mètres où les fractures et macropores augmentent la conductivité jusqu’à 1000 m/an. La transpiration dans les bordures des zones humides provoque des infiltrations et un flux latéral d’eau souterraine superficielle depuis les lacs des zones humides à travers les zones de haute conductivité, ce qui affecte fortement la balance hydrique. Au contraire, les flux souterrains dans les parties profondes et les moraines glaciaires de faible conductivité ont un effet mineur sur le bilan hydrique mais une forte influence sur la salinité du fait que les directions de flux déterminent si les sels s’accumulent dans les zones humides où s’ils sont lessivés vers les zones humides. La compréhension du rôle des aquifères de faible et grande profondeur permettra d’améliorer le schéma conceptuel pour la gestion des écosystèmes des zones humides.

Resumen

Los humedales del norte de Estados Unidos y Canadá existen en numerosas depresiones topográficas en un paisaje de origen glacial. Con respecto al drenaje superficial, los humedales están conectados entre sí la mayor parte del tiempo. El balance de agua en un humedal está controlado por el derretimiento de nieve, la interacción con agua subterránea, y ocasionalmente conexiones de tipo “llenado/vertido” hacia otros humedales. La salinidad y la variabilidad estacional del nivel de agua de estos humedales tienen una fuerte influencia en el ecosistema. El “till” glacial rico en arcilla, que cubre la mayor parte de la región, posee una conductividad hidráulica muy baja (0.001–0.01 m/año), excepto para los metros superiores donde las fracturas y macroporos incrementan la conductividad hasta 1000 m/año. La transpiración en la margen del humedal induce infiltración y flujo lateral de agua subterránea poco profunda desde lagunas a través de zonas de alta permeabilidad, lo que afecta fuertemente el balance de agua en los humedales. En contraste, el flujo de agua subterránea en el “till” más profundo y de baja permeabilidad tiene efectos menores en el balance de agua, aunque una influencia mayor en la salinidad dado que la dirección del flujo determina si las sales se acumulan en el humedal (flujo ascendente) o percolan hacia abajo (flujo descendente) debajo del humedal. Entender los roles de los sistemas de flujo subterráneo profundo y poco profundo mejorará el marco hidrológico conceptual para el manejo de ecosistemas de humedales.

Resumo

As planícies húmidas do norte dos EUA e Canadá existem em numerosas depressões topográficas da paisagem gelada envolvente. No que respeita à ligação com os sistemas de drenagem superficial, essas zonas húmidas não estão inter-ligadas durante a maior parte do tempo. O balanço hídrico das zonas húmidas é controlado pelo escoamento superficial durante o degelo nas zonas elevadas circundantes, pela precipitação, pela evapotranspiração, pelo escoamento de água subterrânea e por transvazes ocasionais de outras zonas húmidas. A salinidade da água e a variação sazonal do nível de água nessas zonas húmidas exercem uma forte influência sobre o ecossistema. Os depósitos argilosos de origem glaciar (tills) que formam a cobertura sedimentar em grande parte da região, possuem condutividade hidráulica muito reduzida (0.001–0.01 m/ano), excepto na zona superficial, em que as fracturas e macro-poros aumentam a condutividade para valores até 1000 m/ano. A transpiração nas margens das zonas húmidas induz infiltração e escoamento lateral das águas subterrâneas pouco profundas das zonas dos lagos e através da zona de maior condutividade, afectando seriamente o balanço hídrico das zonas húmidas. Por contraste, o escoamento das águas subterrâneas nos níveis mais profundos, nos tills de menor condutividade, tem um efeito mínimo sobre o balanço hídrico, mas exerce grande influência na salinidade das águas pois a direcção de fluxo determina se a salinização se acumula nas zonas húmidas (fluxo ascendente) ou é dissipado (fluxo descendente) sob as zonas húmidas. A compreensão da influência dos sistemas de água subterrânea de maior e menor profundidade permitirá melhorar o enquadramento hidrológico conceptual para a gestão dos ecossistemas das zonas húmidas.

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Acknowledgements

Many people have contributed and many are still contributing to the hydrologic studies of prairie wetlands. We particularly want to acknowledge the work of J.B. Millar, whose persistence and dedication in long-term monitoring of water level data enabled us to gain significant insights into wetland hydrology. Although the opinions expressed in this paper are our own, we have benefited greatly from discussions with graduate students, technical assistants, and especially our partners in the wetlands work, Malcolm Conly and the late Bill Stolte. The field research program at the St. Denis National Wildlife Area was supported by Ducks Unlimited Canada, Natural Sciences and Engineering Research Council, Environment Canada Science Horizons Program, and the Climate Change Action Fund. Constructive comments by the three anonymous reviewers and the Guest Editor improved the quality and focus of the paper.

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Correspondence to Masaki Hayashi.

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Part of the material in this paper has been published in the Proceedings of the 36th International Association of Hydrogeologists Congress, Toyama, Japan, October 26–November 1, 2008.

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van der Kamp, G., Hayashi, M. Groundwater-wetland ecosystem interaction in the semiarid glaciated plains of North America. Hydrogeol J 17, 203–214 (2009). https://doi.org/10.1007/s10040-008-0367-1

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