Waiology

Dr Daniel Collins is a hydrologist at NIWA. He formed the Waiology blog to bring together commentary on New Zealand's freshwater systems. The blog features commentary from numerous contributors.

New Zealand captures over 10% of its freshwater resource - Waiology

Feb 12, 2015

By Daniel Collins Following a recent Timaru Herald article (3 February, 2015), I learned of a claim that 98% of NZ’s rainfall is left to flow out to sea, and that we only capture the other 2%. ‘‘This country doesn’t have a water shortage issue. What it has is a water storage issue. We capture a mere 2 per cent of our country’s total rainfall, the rest pours out to sea!’’ – Waitaki MP Jacqui Dean’s office. ‘‘It is wasteful that we only capture around 2 per cent of rainfall in New Zealand, with the rest roaring out to sea.’’ – Minister for Primary Industries Nathan Guy, in a speech to Crown Irrigation Investment Ltd. These statements aren’t quite right, but because the topic is of vital importance, it is worth commenting on what is actually happening. Some of the … Read More

The natural history of New Zealand’s freshwaters: Series conclusion and reader feedback - Waiology

Dec 09, 2014

By Daniel Collins Over the past two months, Waiology’s Freshwater in Focus series on natural history has published 14 articles, from 13 authors and seven institutions, describing the diversity, complexity, and beauty of New Zealand’s freshwaters. From atmosphere to lithosphere and mountain to coast, we have seen examples of how water shapes the landscapes and ecosystems, and what traits plants and animals have acquired to thrive and survive in these environments. The articles highlight the wonder of the natural world – whether for curiosity’s sake or to better under our natural heritage and resources. Waiology will continue to publish articles along these lines, of course, but we will now return to regular programming. If you would like to give feedback on the series or Waiology in general, see below. And for ease of reference, here is a list of the … Read More

The secret lives of freshwater mussels - Waiology

Dec 05, 2014

By Kevin J Collier and Sue Clearwater You may not see them, but they are probably out there somewhere…hiding under overhangs and around fallen branches out of the main flow along stream banks, or buried in soft sediments on lake bottoms with only their siphons showing. And where you find one freshwater mussel there are likely to be more, sometimes many more. Part of a bed of freshwater mussels quietly doing their thing 24/7. The inhalant siphon is fringed with tentacle-like sensory cilia and will occasionally “cough out” clumps of pseudo-faeces comprised of particles that have been rejected for ingestion. (Credit: Bruno David, Waikato Regional Council.)The cryptic[1] habits of these mussels belie their ecological significance. They are ecosystem engineers – when present in large numbers they filter impressive volumes of water, transform carbon and nutrients, oxygenate sediment as they … Read More

Food webs: Who eats who, and what does that tell us? - Waiology

Dec 02, 2014

By Elizabeth Graham Food webs are maps of “who eats who” within an ecosystem (Figure 1a). Each node, or point, in the web represents a species or group of organisms; nodes are connected by a link if there is a known feeding relationship between the two groups. Though they are built on simple predator-prey relationships, food webs integrate complex information about biotic communities and key ecosystem processes, such as energy and nutrient flow, and are increasingly being used to study both biodiversity and function of freshwater ecosystems. Stream food web (a) before and (b) after trout invasion. The size of an organism indicates the relative population biomass of that species (based on reported results from a field experiment conducted in the Shag River in central Otago; Flecker and Townsend 1994). The dashed line indicates a trophic cascade effect of … Read More

Lamprey – Living fossils in our midst - Waiology

Nov 20, 2014

By Cindy Baker Lamprey and hagfish (known as cyclostomes or agnathans) are the only living jawless vertebrates. Over 360 million years old, lampreys swam past herds of drinking dinosaurs, and have survived at least four mass extinctions. The brain of the lamprey is believed to be the closest example of our primal vertebrate ancestors, and lampreys provide important insight into the evolution of fins, jaws and the skeleton, plus vertebrate motor control, and immunology. The oral ‘sucker’ that lamprey use to attach to objects and fish.Lamprey have evolved to utilise the same lifestyle as salmon, freely moving between marine and freshwater environments – and being successful in both. A key difference from salmon is the metamorphosis between life-stages. The larvae (termed ammocoetes) live in the sediments of their natal stream filter-feeding on benthic algae, microbes and other organic material. Read More

How many whitebait eggs does it take to make a whitebait fritter? - Waiology

Nov 17, 2014

By Paul Franklin Every spring New Zealanders can be found creeping out at the crack of dawn to line the lower reaches of our rivers in the hope of catching that New Zealand delicacy – whitebait! As the mist lifts and the fishing comes to an end for the day, conversations turn to that critical question… what’s the best recipe for whitebait fritters? I don’t claim to have the answer to that, but I do hope to provide some insight into how many eggs might be needed… and the answer might just surprise you! A whitebait fritter.Whitebait are the juveniles of five species of native fish (see Amber McEwan’s article for more details), returning to freshwater after spending the first few months of their lives at sea. This migration into freshwater is a critical part of their life-cycle, … Read More

Delving deeper: Life below the bottom of the stream - Waiology

Nov 13, 2014

By Aslan Wright-Stow Streams and rivers are typically thought of in two dimension space, flowing from upstream to down, from high in the catchment and then out to sea. Delve a little deeper however and we find a third dimension – a vertical space underneath the streambed that’s home to many freshwater invertebrates. Linked hydrologically to the overlying water column, the hyporheic zone sits underneath what is typically considered the bottom of a stream or river and links groundwater to surface water. Given the inability for simple direct observations and difficulties in sampling the hyporheic zone, research into this ecosystem didn’t really start until the mid-1990s. Common study techniques include sampling biota by pumping hyporheic water and animals from wells sunk to different depths, freeze-coring vertical profiles by pumping liquid nitrogen or dry ice down a steel well and extracting … Read More

Carbon cycling in mountain ranges – Our environmentally friendly Southern Alps - Waiology

Nov 10, 2014

By Sarah Mager The Southern Alps of New Zealand are the source of some of New Zealand’s most iconic river systems.  The development of the South Island has been intimately connected with these powerful water sources. For instance, the Clutha initially provided a critical navigation route into Central Otago and the early gold fields; the Waitaki sustains eight hydroelectrical power stations that were crucial to developing a power-hungry growing nation; the Waimakariri, Rakaia and Rangitata all provide large water sources to the Canterbury Plains, both as surface and groundwater resources, and are critical to pastoral development and the rapid expansion of dairy production in the region.  All of these rivers are driven by the interplay between atmospheric processes and the resultant uplift along the tectonic plate boundary.  In geological terms, the Southern Alps are one of the fastest uplifting mountain … Read More

Understanding the natural history of New Zealand’s nutrient fluxes - Waiology

Nov 06, 2014

By Emily Diack and Sarah Mager Water quality in New Zealand has been a hot topic of late, especially when it comes to the growing impact that agriculture and land use changes are having on our waterways. Maintaining good water quality is fundamental for sustaining our indigenous ecosystems, but how do we define what that ‘good’ level of water quality is? The transformation of New Zealand’s vegetation cover and land use has had a significant impact on the functioning of freshwater ecosystems and water quality, with local waterways becoming increasingly subject to pollution and nutrient overloading. Over the past century agriculture in New Zealand has intensified from low density grazing to large-scale dairy and crop farming, and population increases have caused extensive urbanization. These developments and alterations of original land uses, to a new state, are dramatically disrupting freshwater systems … Read More

Hapua: developments in understanding river mouth lagoons and their responses to freshwater regimes - Waiology

Nov 03, 2014

By Deirdre Hart Hapua are a type of predominantly freshwater river mouth lagoon that occurs on high energy temperate coasts. In New Zealand, they comprise a group highly-dynamic and socio-culturally important environments (Figure 1). Hapua behave differently to lagoons with tidal prisms. This means that classic estuary models cannot be applied to their understanding or management. Over the last three decades there have been significant advances in our understanding of hapua systems, with new concerns arising regarding the effectiveness of recent management regimes. This article briefly highlights key advances and gaps in our knowledge of these significant rivermouth lagoon systems. Figure 1. The hapua lagoon interface between the Hurunui River and the high-energy north Canterbury mixed sand and gravel coast is a popular site for weekend fishing and recreation.Hapua behaviour Hapua comprise coastal conveyor belts for freshwaters and sediments … Read More