How to age wa­ter & why it’s im­por­tant

New sci­ence is telling us about the age of the wa­ter in our lakes and rivers, and it ex­plains why things may get worse be­fore they get bet­ter.

NZ Lifestyle Block - - Our Water - WORDS ABBY MATTHEWS

Akey chal­lenge for re­source man­agers and com­mu­ni­ties is pre­dict­ing how the world might look 10, 20 or even 50 years from now. De­ci­sions we make and ac­tions we take all lead to out­comes, some that can be dif­fi­cult to fore­see or pre­dict.

Strik­ing the bal­ance be­tween en­abling growth and pro­tect­ing the en­vi­ron­ment gen­er­ates ten­sion within com­mu­ni­ties. Many ap­pear to be striv­ing to­ward the same goal, but in re­cent years we have seen dis­agree­ments arise over the pace or scale of change, or the mech­a­nisms re­quired for us to reach a com­mon end. So­cial, eco­nomic and cul­tural val­ues that we hold dear also come into play and add fur­ther com­plex­ity to de­ci­sion mak­ing.

How­ever, chal­lenge is of­ten ac­com­pa­nied by op­por­tu­nity. Ad­vances in sci­ence and tech­nol­ogy con­tinue to pro­vide new tools and tech­niques that can im­prove our un­der­stand­ing of our en­vi­ron­ment and help us man­age our nat­u­ral re­sources in a sus­tain­able way.

One group lead­ing the way is the ded­i­cated team of sci­en­tists at Te Pu Ao, GNS Sci­ence, which has de­vel­oped one of the most ac­cu­rate age dat­ing lab­o­ra­to­ries in the world.

Wa­ter dat­ing is emerg­ing as an im­por­tant tool for wa­ter man­age­ment in New Zealand. Novel tech­niques us­ing iso­topes and trac­ers found in wa­ter have a range of ap­pli­ca­tions. They can help us un­der­stand nat­u­ral and hu­man im­pacts on wa­ter qual­ity, iden­tify ar­eas where ground­wa­ter sys­tems are re­plen­ished, and how long wa­ter takes to travel to lakes, rivers or the sea. These tech­niques can also help us iden­tify ar­eas of in­ter­ac­tion be­tween ground and sur­face wa­ter. This is im­por­tant for man­ag­ing the ef­fects of land use on wa­ter qual­ity.

One ex­am­ple is radon which is now be­ing used to map ar­eas of ground­wa­ter in­flow into wa­ter­ways in NZ.

Radon is a ra­dioac­tive gas that oc­curs nat­u­rally in rocks and soils. It is trans­ported by wa­ter un­der­ground, de­te­ri­o­rat­ing quickly when it is ex­posed to the at­mos­phere. The pres­ence of radon tells us where ground­wa­ter is en­ter­ing wa­ter­ways. This is im­por­tant for track­ing the flow of wa­ter through a catch­ment, and also the nu­tri­ents and con­tam­i­nants that can ac­com­pany it.

Radon Tri­tium is an iso­tope of hy­dro­gen that forms in the at­mos­phere and is trans­ported via rain­fall onto land and into our rivers, lakes and ground­wa­ter sys­tems. Tri­tium iso­topes de­cay at a known rate, which means that the amount of tri­tium in a sam­ple can be used to cal­cu­late the av­er­age age of the wa­ter. Tri­tium is mea­sured in sur­face and ground­wa­ter, and in­ter­preted by sci­en­tists us­ing flow mod­els to es­tab­lish the av­er­age age of the wa­ter.

Age and chem­istry can tell us about the jour­ney of wa­ter: where it has come from, how far it has trav­elled, and how long it will take to see wa­ter qual­ity re­spond to man­age­ment in­ter­ven­tions.

Wa­ter dat­ing has be­come an im­por­tant tech­nique in de­vel­op­ing man­age­ment ap­proaches for wa­ter re­sources in NZ. In Lake Ro­torua, wa­ter can take around 60 years to travel from the sur­round­ing catch­ment, through large vol­canic aquifers, and into the lake.

By con­trast, ground­wa­ter dis­charg­ing into gravel-bed rivers such as the Man­gatain­oka River near Pahiatua (20km east of Palmer­ston North) can be very young, just a year or two old. The dif­fer­ence be­tween the two travel times high­lights the im­por­tant role that ge­ol­ogy plays in the trans­port of wa­ter and nu­tri­ents, par­tic­u­larly ni­tro­gen which can con­trib­ute to al­gal growth in rivers and lakes.

In time, im­prove­ments may be seen, but in some catch­ments wa­ter qual­ity is likely to get worse be­fore it gets bet­ter, even when im­prove­ments are be­ing made. In oth­ers, pos­i­tive change will be more im­me­di­ate.

There is no one-size-fits-all man­age­ment ap­proach that is ap­pro­pri­ate for all our rivers, lakes, es­tu­ar­ies and aquifers. Catch­ments are unique and the best so­lu­tions can only be de­vel­oped with a sound un­der­stand­ing of the en­vi­ron­ment around us. There’s in­creas­ing pres­sure on our wa­ter­ways and that means a need for new and novel ap­proaches to fill the gaps in our knowl­edge. By in­vest­ing in tech­niques such as age dat­ing, we can en­sure that catch­ment man­age­ment de­ci­sion-mak­ing is in­formed by sci­ence.

The more ad­vanced our sci­en­tific tool box, the bet­ter equipped we are to man­age our en­vi­ron­ment sus­tain­ably.

ABBY MATTHEWS is an en­vi­ron­men­tal sci­en­tist, and the sci­ence and in­no­va­tion man­ager for Hori­zons Re­gional Coun­cil.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.