Small artificial impoundments have big implications for hydrology and freshwater biodiversity

Abstract

Headwater streams are critical for freshwater ecosystems. Global and continental studies consistently show major dams as dominant sources of hydrological stress threatening biodiversity in the world’s major rivers, but cumulative impacts from small artificial impoundments concentrated in headwater streams have rarely been acknowledged. Using the Murray Darling River basin (Australia)and the Arkansas River basin (USA) as case studies, we examine the hydrological impact of small artificial impoundments. The extent of their influence is significant, altering hydrology in 280 - 380% more waterways when compared to major dams alone. Hydrological impacts are concentrated in smaller streams (catchment area < 100 km2), raising concerns that the often diverse and highly endemic biota found in these systems may be under threat. Adjusting existing biodiversity planning and management approaches to address the cumulative effects of many small and widely distributed artificial impoundments presents a rapidly emerging challenge for ecologically sustainable water management.

Explaining changes in rainfall–runoff relationships during and after Australia's Millennium Drought: a community perspective

“…Farm dams, also known as farm ponds, are small private dams located on hillsides, drainage lines, or small streams. Individual dams typically harvest only small volumes, but collectively, the impact can be large (Habets et al, 2018;Morden et al, 2021). Thus, the total water storage capacity of all dams in a watershed may be an important index, particularly when relativised by precipitation or streamflow to account for aridity; that is, a given storage size may have a higher relative impact in drier areas (e.g.…”

“…Volumetrically, water harvesting by farm dams is greatest during moderate and high flows, but if expressed in relative terms, impacts are greatest during the dry season and during dry years (Morden et al, 2021). Flow impacts occur due to both extracted water (for stock, domestic, or irrigation use) and evaporated water being unavailable to flow downstream.…”

Explaining changes in rainfall-runoff relationships during and after Australia's Millennium Drought: a community perspective

“…Farm dams, also known as farm ponds, are small private dams located on hillsides, drainage lines, or small streams. Individual dams typically harvest only small volumes, but collectively, the impact can be large (Habets et al, 2018;Morden et al, 2021). Thus, the total water storage capacity of all dams in a watershed may be an important index, particularly when relativised by precipitation or streamflow to account for aridity; that is, a given storage size may have a higher relative impact in drier areas (e.g.…”

“…Volumetrically, water harvesting by farm dams is greatest during moderate and high flows, but if expressed in relative terms, impacts are greatest during the dry season and during dry years (Morden et al, 2021). Flow impacts occur due to both extracted water (for stock, domestic, or irrigation use) and evaporated water being unavailable to flow downstream.…”

“…Estimates of farm dam growth have recently been produced (Malerba et al, 2021), and the next step is to use such estimates in modelling (e.g. Fowler et al, 2015;Morden et al, 2021) to quantify the additional impact during the Millennium Drought relative to earlier droughts.…”