The Troubled Waters of the Vernon Lagoon

Forest and Bird, Issue 314, 1 November 2004, Page 28

The Troubled Waters of the Vernon Lagoon

DAVE HANSFORD

looks ata

threatened wetland in Marlborough.

his is an unlovely place. Mounds of | dumped tyres, spilling into the Wairau Estuary, mark the end of the road from Spring Creek. A pair of rusting Holdens, held fast by tendrils of boxthorn, will never make the trip back to town. A sign warns against eating the shellfish. The Wairau River dodges the silvered corpses of drowned macrocarpas and a couple of derelict dinghies before rushing headlong between banks of greywacke boulders into Cloudy Bay. Piles of dumped household rubbish threaten to join it in the next stiff breeze. There are other middens here, where Marlborough meets the sea. Detritus dating back perhaps 1000 years marks where the moa hunters killed flocks of their staple prey. The giant, flightless birds were rounded up high in the Vernon Hills just south of here, or on the distant reaches of the Wairau Plain

to the west and driven along the narrow boulder bank that separates the Wairau lagoons from the open sea. The end came at the blunt spit by the rivermouth, where the Wairau cut off any escape. Moa bones still lie scattered across the hunters’ former camps, along with their instruments, and old fire pits. In the 1950s, archaeologist Roger Duff began turning over stones here. By the end of his excavations, he’d discovered 18 sites — now listed with the Historic Places Trust — and added volumes to our understanding of prehistoric New Zealand. As a seasonal base for what Duff called a ‘fishing and fowling economy, the Wairau lagoons — nowadays known also as the Vernon Lagoons — were ideal. Flocks of now-extinct New Zealand swan and a richness of ducks made for feasting and plenty during the moult; and the Wairau

teemed with spawning whitebait and kahawai. The entrance was a trove of shellfish. Fires were set on a limitless supply of driftwood. Today, it’s more difficult to see the value people place on the lagoons. They’re a receptacle, mostly for trade waste, sewage effluent, wastewater — if Marlborough has any to waste. There are a few walking tracks, but they start from Blenheim’s reeking oxidation ponds, which deter all but the hardiest. The birds, however, are grateful for lagoons, degraded or not. Wading birds, mostly; local and international. Native swan — and moa — are long gone, but hunters still come here. Their rickety maimai dot the shallow lagoons behind the boulder bank, where shotgunners lie in wait for mallard, shoveller and grey duck. Vaughan Lynn is the Marlborough field officer for Fish and Game. He says the lagoons

are the most important recreational hunting asset in the region, and account for around 400 licences every year. Fish and Game and the Department of Conservation have drawn up a ‘code of conduct} which urges hunters to make sure they're not drawing a bead on a protected species, or firing at a bird so distant that they will only leave it wounded — a practice known as ‘skybusting’ The biggest management issue of late has seen lead shot banned from ammunition in favour of non-toxic steel pellets. Studies showed that 30 percent of mallards in New Zealand had traces of lead in their blood, from ingesting shotgun pellets left behind in the mud where they dabbled. After a four-year phase out, lead pellets are now illegal, and rangers are out in the lagoons each season to make sure everyone is abiding by the rules. While they’re out there, they keep a watch

for coarse fishers — those who eschew trout and salmon in favour of species like perch, rudd, carp and tench. It is illegal to either release or fish for these animals in Nelson/Marlborough. That hasn’t stopped a rash of illicit liberations in the region, which has put native fish and ecosystems under real pressure. Vaughan Lynn says that if they found their way into the Wairau lagoons, coarse fish — along with the tiny, dreaded gambusia, or mosquito fish — would have a devastating impact on a wetland already under stress. Vaughan Lynn says the estuary is getting shallower every year since the Marlborough District Council diverted away half the flow of the Wairau River to protect nearby Blenheim from floods. He says the situation will only get worse if a proposal to take more water from the upper Wairau for a hydro scheme gets the nod.

Trustpower says it wants to take water from Birch Hill, on the river’s upper reaches, and run it through a series of hydro dams and canals before returning it 46 kilometres downstream at Marchburn. That is anathema to Fish and Game, which teamed up last June with Forest and Bird, the Marlborough Environment Centre and various anglers’ clubs to fight it. "We have major concerns with that scheme, says Vaughan Lynn, ‘both over the amount of water they want to take out, and the flow they intend to leave’ He says Trustpower means to maintain a residual flow of 10 cumecs for seven months of the year, a figure well below the river’s median flow of 70 cumecs, and that would have serious consequences for the river’s instream values and invertebrate productivity. "Trustpower’s own report predicts a 20-25 percent reduction in food for the birds along

the river, he says. "Black-billed gulls and 25 percent of the world population of blackfronted terns live and breed along that stretch? In addition, the Wairau Valley Water Enhancement Scheme has applied for consents to take another 3.3 cumecs from the river, and another irrigation project, (the Marlborough Water Augmentation Group proposal), which stalled in 2003, has since been resurrected. Vaughan Lynn is concerned that lower flows would stop fish, like the Wairau’s trophy brown trout, making their upstream spawning runs. Malcolm Brennan, a programme manager with the Department of Conservation in Renwick, doesn’t think the schemes would affect the lagoons themselves to any great degree because, he says, the water would be returned to the Wairau well before it flows into them. But he says there’s no shortage of other threats, namely the thickets of boxthorn, gorse, barberry, marram, broom, mallow and sweet briar that throng the boulder bank and lagoon flats. Programmes to deal with the boxthorn and gorse are now well advanced, as is the war on the wattles that threaten the lagoon’s islands, but he says there’s constant reinvasion from neighbouring properties, and the endless

seed source that floats down from the Wairau Plain. Brian Bell is the Marlborough representative for the Ornithological Society of New Zealand. He used to patrol the lagoons by bicycle as a Wildlife Service ranger in the 1950s. ‘It was a difficult place to work, he recalls. ‘You'd hit one of those Maori canals and disappear up to your waist in mud and water. It is still a difficult place to work in, which he says is one reason why we still know so little about it. ‘Even now, I don’t think we know the full importance of the lagoons . .. we don’t even have an accurate census for most bird species. Brian Bell says it’s the resident breeders — the dotterels, the shags, the terns and the spoonbill — that make the place so special. It is also an important stopover for local migrants, such as wrybill and black stilt; and global travellers such as golden plover, turnstone and godwits. Some of the smaller saltmarsh lagoons on the northern side of the Wairau mouth used to host more exotic vagrants too — lesser yellowlegs and sharp-tailed sandpiper — before they were drained. Today, a few pied stilt still fossick about there in the mud, now

black and anaerobic, but the gorse is crowding them in and the area is shredded by four-wheel-drive tracks. There are even wheel marks through the ponds themselves. Malcolm Brennan of DoC says a priority is to get water flowing through them again. (The Marlborough District Council has offered to fund the culverts if DoC gets the consents.) He sees a need to restore the freshwater processes that have been lost, not just here, but throughout the more than 2000 hectares of lagoon and saltmarsh turfs that make up the greater Wairau lagoons. A DoC report released in August charges that the Wairau Diversion denied the wetlands much of the freshwater flushes they need; and more salt water flows in since the sandbar at the estuary mouth was removed as a further flood precaution. It says the lagoons nearest the water channels have lost much of their margins to erosion, while deforestation in the Wairau catchment means they’re getting shallower as soil is carried in and dumped by the river. When that happens, water temperatures start climbing, and once-extensive beds of eelgrass are being replaced by algae. No one has measured the impacts of pollution from Blenheim or from intensive farming along the lower river. Until recently the Blenheim freezing works discharged directly into the lagoons. The city’s oxidation ponds — recently doubled in size after Renwick was brought onto reticulated sewerage — still do. Studies of estuarine invertebrates in the 1990s found very low diversity — a sign the lagoons are under stress. Fish and Game has moved to get more freshwater running back into the lagoons. It has already re-watered a wetland, Copp’s, on the true right of the Opawa, which Vaughan Lynn says will stay closed to shooters. And he has a few other ideas. ‘There’s potential to uncap a couple of old artesian bores downstream of Morgan’s Creek to create some more freshwater wetlands. The birds would flock to them?

ter is becoming an increasingly scarce commodity in the region, and priorities have to be drawn, according to Brin Williman, a river and drainage engineer with the Marlborough District Council. He says the soaring thirst of vineyards has put Marlborough’s groundwater under enormous pressure, and the council’s first concern is to ensure adequate supplies for industrial and domestic users. Besides, he’s not at all sure that the lagoons are suffering a shortage of fresh water. In fact, he maintains they receive very little in the first place. ‘I suspect the fresh water goes out to sea.’ Brin Williman says the ratio of saltwater to fresh in the lagoons could be as high as 10 to one, and that way any changes the Council might make to the Wairau Diversion would probably have little impact on salinity. He points out that in former times, the rivermouth was periodically blocked, sometimes for weeks, by longshore drift of sediment driven north by the wind and currents. ‘When that happened, water would be held at high-tide levels in the lower reaches until the river forced a new exit further north. Brin Williman says the lagoons and their inhabitants would once have been subjected to huge fluctuations in both flow and salinity. "They would have been very difficult conditions for any fauna or flora to operate in. In 1960, the Harbour Board built those boulder walls the car wrecks are parked on at the Wairau entrance, which put a stop to the river’s meanderings once and for all. Brin Williman says that’s benefited nature and humans alike. ‘For the last 44 years, we’ve had a very stable situation; there’s a full tide every day, and more thorough mixing than previously. For him the issue is not the mix, it’s the quality. ‘Winery effluent is increasing markedly, he says, ‘as is the total amount of trade waste going through our system now. He says canoeists have complained of cuts turning septic in the Wairau’s low summertime flows. Murray Brennan of DoC says many management initiatives — like better public access and interpretation — will have to wait until the Maori Land Court awards mana whenua over the lagoons to one of the seven tribes contesting it. ‘It makes co-management difficult; he says. ‘We can’t put any signs up yet, because that might be taken as meaning that DoC recognises the mana whenua of a particular iwi. In a sense, the future of the Wairau Lagoons is in a similar stalemate. Their every need seems to be at the bottom of a priority list,

topped by the local economy — and water. For now, the lagoons seem to be ticking over. DoC is trying to keep pace with the weeds, but if they’re ever going to resemble

the ‘fishing and fowling paradise they once were, someone needs to make a start. Soon.

— DAVE HANSFORD

of Origin Natural History Media

is a Wellington-based writer and photographer.