Improving climate change resilience and reducing

Improving climate change resilience and reducing sediment runoff through better mangrove management in Princess Charlotte Bay

Mackenzie, J. & Duke, N.C. July 2015

` Improving climate change resilience and reducing sediment runoff through better mangrove management – TropWATER July 2016

Improving climate change resilience and reducing sediment runoff through better mangrove management in Princess Charlotte Bay A Report for Balkanu Cape York Development Corporation (Balkanu) As part of the National Landcare Programme funded Mangrove Watch in East Normanby Basin with Kalpowar Land Trust Project

July 2016 Prepared by Jock Mackenzie & Dr Norm Duke MangroveWatch Science Hub Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) ATSIP Building James Cook University Townsville Qld 4811 Phone: (07) 4781 6708 Email: [email protected] Web: www.jcu.edu.au/tropwater/ www.mangrovewatch.org.au

2


Information should be cited as: Mackenzie, J & Duke, N.C. 2016. Improving climate change resilience and reducing sediment runoff through better mangrove management. MangroveWatch Science Hub, Centre for Tropical Water & Aquatic Ecosystem Research. Publication, James Cook University, Townsville. 80pp. For further information contact: MangroveWatch Science Hub Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) James Cook University [email protected] ATSIP Building Townsville Qld 4810 (07) 4781 6708 This publication has been compiled by the Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), James Cook University. © James Cook University, 2016 Except as permitted by the Copyright Act 1968, no part of the work may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without the prior written permission of TropWATER. The information contained herein is subject to change without notice. The copyright owner shall not be liable for technical or other errors or omissions contained herein. The reader/user accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information. Enquiries about reproduction of information used within this report should be directed to [email protected] ACKNOWLEDGEMENTS This project was funded through an Australian Government Reef Rescue Systems Repair Grant, under then National Landcare Programme. This project was made possible through the excellent coordination and project management of Balkanu Cape York Development Corporation. The data presented herein was collected in partnership with Traditional Owners of the Kalpowar Native Title Area, with support from the Alka-Bawar Land Trust. We thank the Traditional Owners and Alka-Bawar Land Trust for their on-going engagement and support of this project. TABLE OF CONTENTS

3


Acknowledgements.................................................................................................................... 3 Table of contents........................................................................................................................ 3 Executive Summary ................................................................................................................... 4 Program Overview ..................................................................................................................... 5 Program Background ................................................................................................................. 6 Tidal Wetland Indicators of Sea Level Rise in Princess Charlotte Bay .................................. 11 Case Study 1: Shoreline Retreat .......................................................................................... 12 Summary of Activities Undertaken to Date..................................................................... 12 Key Findings .................................................................................................................... 13 Introduction...................................................................................................................... 14 Methods ........................................................................................................................... 16 Results.............................................................................................................................. 20 Discussion ........................................................................................................................ 30 Case Study 2. Within tidal wetland change – zonal shift and mangrove-saltmarsh dynamics ............................................................................................................................................. 35 Summary of Activities Undertaken to Date..................................................................... 36 Key Findings .................................................................................................................... 36 Methods ........................................................................................................................... 38 Results.............................................................................................................................. 39 Discussion ........................................................................................................................ 42 Case Study 3: Estuarine Shift .............................................................................................. 44 Achievements 2015 ......................................................................................................... 45 Key Findings .................................................................................................................... 45 Introduction...................................................................................................................... 45 Methods ........................................................................................................................... 46 Results.............................................................................................................................. 48 Discussion ........................................................................................................................ 48 Case Study 4: Upland Migration and Terrestrial Retreat .................................................... 51 Achievements 2015 ........................................................................................................ 52 Key Findings .................................................................................................................... 53 Methods ........................................................................................................................... 54 Results.............................................................................................................................. 58 Discussion ........................................................................................................................ 64 Case Study 5: Anthropogenic Drivers of Change - Vehicles, Cattle and Pigs .................... 67 Methods ........................................................................................................................... 67 Results.............................................................................................................................. 69 Discussion ........................................................................................................................ 70 References................................................................................................................................ 74 EXECUTIVE SUMMARY This report presents the current understanding of tidal wetland dynamics, shoreline processes and threatening process within Princess Charlotte Bay based on the data collected during 2014 and 2015 for the MangroveWatch in East Normanby Basin Reef Rescue System Repair Project. The report also presents a summary of field activities undertaken during 2015 with preliminary results.

4


PROGRAM OVERVIEW The MangroveWatch East Normanby Basin Project was initiated in 2014 as a partnership between Balkanu Cape York Development Corporation (Balkanu), James Cook University (JCU) MangroveWatch and the Traditional Owners of the Alka-Bawar Land Trust to address ongoing and emerging natural resource management issues in the extensive tidal wetland systems of eastern Princess Charlotte Bay that threaten the health and resilience of the Great Barrier Reef (GBR). Recent reports by Brooks et al. (2013) and others (Howley et al., 2013) have highlighted potentially large sediment inputs to the Northern GBR originating from erosion of tidal wetland systems in Princess Charlotte Bay. Whilst processes underpinning this large-scale sediment export are likely to be natural, they are potentially exacerbated by human stressors that damage sensitive tidal wetland habitat, including, vehicle damage, cattle grazing and feral pigs. Furthermore, Princess Charlotte Bay (PCB) tidal wetlands and adjacent freshwater wetlands are vulnerable to climate change driven sea level rise and increased severe storm frequency. Climate change related processes will potentially increase sediment export to the GBR from PCB coastal systems. Tidal wetlands have the capacity to ‘keep pace’ with sea level rise and withstand climate change impacts, buffering future sediment export, provided they are in a healthy state (Gilman et al., 2008). Direct human impacts and high levels of nutrient delivery to tidal wetland systems in PCB may reduce the resilience of tidal wetlands to climate change (Kirwan and Megonigal, 2013) leading to nett loss of tidal wetland cover and function, and ultimately, increased sediment delivery to the GBR. In 2006, the Eastern Normanby region of PCB was returned to Traditional Owner management and is now administered by the Alka-Bawar Land Trust. This presented an opportunity for Traditional Owners to undertake direct on-ground action to address impacts to tidal wetland habitats in Eastern Princess Charlotte Bay, enhancing ecosystem value, improving ecosystem resilience, and reducing sediment delivery to the Northern GBR. On-ground actions to be delivered by this program are fencing to reduce cattle access and improve cattle grazing management, and fencing and road realignment to reduce vehicle impacts to tidal wetland areas. On-ground actions are to be informed by extensive assessment of tidal wetland habitat structure, condition and value to identify high-value and highrisk tidal wetland protection priority areas. Tidal wetland condition assessments provide insight into the functional capacity of tidal wetlands to buffer sediment export and highlight issues that may reduce tidal wetland resilience to inform broader water quality management issues in the Normanby Catchment. Tidal wetland condition assessments are undertaken as a partnership between Traditional Owners and James Cook University tidal wetland specialists, facilitated by Balkanu Cape York Development Corporation. This partnership provides an opportunity to improve GBR water quality by reducing impacts to tidal wetland habitats in PCB, but will also enhance scientific understanding of tidal wetland systems in Northern Australia, including climate change resilience mechanisms and threats. Direct engagement of Traditional Owner landholders in the tidal wetland assessment process will increase understanding of tidal wetland ecology leading to improved future land management in the East Normandy Region, and reduced impacts to the Northern GBR.

5


There are 6 phases of tidal wetland condition assessment to inform and assist on-ground delivery of project outcomes; 1. Traditional Owner training & engagement. 2. Baseline surveys of tidal wetland habitat extent, structure, condition and threats. 3. Groundtruthing baseline survey outcomes 4. Inventory of tidal wetland values, including carbon and sediment buffering capacity. 5. Assessment and monitoring of on-ground action effectiveness in improving tidal wetland condition and reducing sediment export to the GBR. 6. Ongoing assessment of changing habitat condition to understand natural processes, direct drivers of change and catchment-based drivers of reduced tidal wetland ecosystem function and resilience. Here we present a summary of activities and data related to phases 2 & 3 in 2014 and 2015. These results are part of an ongoing project and are therefore subject to refinement as additional data is collected providing greater insight into tidal wetland processes and threats in Princess Charlotte Bay. PROGRAM BACKGROUND Princess Charlotte Bay (PCB) is a wide, shallow embayment in the dry tropics region of north-east Cape York, Queensland (Figure 3). At 50km wide, PCB is one of the largest bays on the Australian coastline. PCB is the receiving waters of the Normanby River catchment, comprising 4 major estuary subcatchments in the coastal plain: North Kennedy, Bizant, Normanby and Marratt. The Normanby River catchment is the 4th largest catchment flowing into the Great Barrier Reef (GBR) Marine Park, covering an area of 24, 226 km2. Catchment landuse within the Normanby Catchment is dominated by cattle grazing (75%) but the catchment retains most (95%) natural vegetation cover (Brooks et al., 2013; Howley, 2013)

Figure 1 Location of Princess Charlotte Bay

6

` Improving climate change resilience and reducing sediment runoff through better mangrove management – TropWATER July 2016 14°16'0"S 14°17'0"S

Princess Charlotte Bay Tidal Wetland Princess CharlotteArea Bay Tidal Wetland Area

14°18'0"S 14°19'0"S

Tidal wetlands within 2km of shoreline

Princess Charlotte Bay Tidal Wetland Area

Tidal Wetlands

14°20'0"S

Princess Charlotte Bay Marratt R Normanby R Bizant R Kennedy R Shoreline

Mangrove Area (ha)

9017

1150

1524

1072

2256

1637

Saltmarsh (ha)

26242

4234

3346

4384

3477

7540

Total Area (ha)

35259

5384

4870

5456

5733

9177

Tidal Wetland Index

0.34

0.27

0.46

0.24

0.65

0.22

14°21'0"S 14°22'0"S 14°23'0"S 14°24'0"S 14°25'0"S 14°26'0"S 14°27'0"S 14°28'0"S 14°29'0"S 14°30'0"S 14°31'0"S 14°32'0"S 14°33'0"S 14°34'0"S

Legend

ratt R

Marratt R

manby R

Normanby R

ant R

Bizant R

nedy R

14°35'0"S 14°36'0"S 14°37'0"S 14°38'0"S

Kennedy R

Charlotte Bay Tidal Wetlands

Princess Charlotte Bay Tidal Wetlands

Wetlands Mapping Program Data 2009

Queensland Wetlands Mapping Program Data 2009

grove

Mangrove

flats and saltmarshes

Salt flats and saltmarshes

4

8

12

Kilometers 16 0 4

8

12

14°39'0"S

Figure 3 Location of Princess Charlotte Bay, Qld. Image from Google Earth

14°40'0"S 14°41'0"S 14°42'0"S

Kilometers 16

14°43'0"S 14°44'0"S

3°47'0"E

143°49'0"E

143°51'0"E

143°53'0"E

143°55'0"E 143°45'0"E 143°57'0"E 143°47'0"E 143°59'0"E 143°49'0"E 144°1'0"E 143°51'0"E 144°3'0"E 143°53'0"E 144°5'0"E 143°55'0"E 144°7'0"E 143°57'0"E 144°9'0"E 143°59'0"E 144°11'0"E 144°1'0"E 144°13'0"E 144°3'0"E 144°15'0"E 144°5'0"E 144°17'0"E 144°7'0"E 144°19'0"E 144°9'0"E 144°21'0"E 144°11'0"E 144°23'0"E 144°13'0"E 144°25'0"E 144°15'0"E

Figure 2 Princess Charlotte Bay tidal wetland area

The Princess Charlotte Bay coastal floodplain represents the largest continuous tidal wetland extent along the East coast of Australia (Danaher, 1995). The 35,259 ha PCB tidal wetlands are comprised of 26,242 ha of mangrove and 9017 ha of tropical saltmarsh habitat (Figure 2). The proportion of mangrove and saltmarsh is typical of dry-tropics intertidal habitats with rainfall of ~1085mm yr-1 (Duke et al. unpub data). However, the extensive area of tidal wetlands provides for much greater habitat diversity than occurs in other dry-tropics tidal wetland complexes. Tidal wetland ecotypes represented in PCB tidal wetlands range from Tall (0.4), sparse vegetation (grass) (0.2-0.4), bare ground (0.1-0.2) and water or wet areas (60%) (Figure 9 & Figure 10). The majority of all shoreline sections were classified as in an eroded state except for the shoreline section between the Bizant and Kennedy Rivers (Bizant). The Bizant shoreline was mostly either stable (30%) or prograding (30%).

Figure 9 Graph of aerial shoreline process classification (% Shoreline)

Shoreline change analysis shows that there has been a nett loss of shoreline along the Princess Charlotte Bay shoreline at a rate of -0.6 ± 0.1 m yr-1 (Figure 11). The rate of shoreline loss is not equal across the bay shoreline with some areas, such as the coastline between the Bizant and Kennedy rivers showing mangrove expansion due to sediment accretion, and other areas such as West of the Kennedy River and between the Normanby and Marratt Rivers, experiencing erosion (Figure 12). Historically the shoreline East of the Normanby River has been relatively stable. The location of the largest overall shoreline retreat was present at the mouth of the Normanby River where 239m of shoreline has been lost since 1970 at a rate of -4.9m yr-1. However this area is small in comparison to the extensive erosion along the coastline West of the Kennedy River where shoreline losses of up to 207m have occurred across a much greater linear expanse of shoreline.

20

143°57'0"E

144°0'0"E

144°3'0"E

144°6'0"E

144°9'0"E

144°12'0"E

¯

Princess Charlotte Bay Shoreline Process 2014

14°15'0"S

143°54'0"E

14°18'0"S

Bathurst Heads

14°21'0"S

Wireyard Ck

Princess Charlotte Bay Marratt River

14°24'0"S

Normanby River

Shoreline Process Classification Extreme Erosion Severe Erosion

Kennedy River

14°27'0"S

Legend

Moderate Erosion

Bizant River

Minor Erosion Exposed

Prograding 0

1.25

25

5

7.5

Kilometers 10

Map of Princess Charlotte Bay showing showing shoreline process classification as determined from aerial survey images 2014

No Data

14°30'0"S

Stable

` Improving climate change resilience and reducing sediment runoff through better mangrove management

Mean Rate of Shoreline Change (m yr-1)

– TropWATER July 2016

Annual Rate of Shoreline Change 1970 to 1991 & 1991 to 2014 1

Kennedy Bizant Normanby Marratt Bathurst Heads Overall

0

-1 -2

ra ve O

ea H

ur

st

M

ll

ds

tt ar

ra

by an m

Ba

th

N

or

Bi za nt

Ke nn ed y

-3

Shoreline Section Figure 11 Graph of mean rates of shoreline change along Princess Charlotte Bay between 1970 and 2014.

Mean rate of shoreline loss across Princess Charlotte Bay increased between 1991 and 2014 (-0.74 ± 0.08 m yr-1) compared to 1970 to 1991 (0.46 ± 0.06 m yr-1) (Table 2). The two-factor analysis of variance (Time period x Shoreline Section) showed a significant effect of time period, F(1,1003 )=5.674, p=0.0174. The rate of shoreline loss was greater between 1991 and 2014 compared to the preceding time period (1970 to 1991). The effect of shoreline location was significant F(1,1003) = 129.8, p0.4), sparse vegetation (samphire, salt couch and algal mat) (0.2-0.4), bare ground (0.1-0.2) and water or wet areas (0.4), and non-mangrove vegetation.

46

143°57'0"E

144°0'0"E

144°3'0"E

Princess Charlotte Bay Bizant River

Estuary Shoreline Change Bizant & Kennedy Rivers 1989 to 2015

14°39'0"S

14°36'0"S

14°33'0"S

14°30'0"S

Kennedy River

144°6'0"E

Pg No

Shoreline Change Mangrove Gain

Stable Mangrove Mangrove Loss 0

0.5

1

2

3

Kilometers 4

Map of Bizant & Kennedy Rivver estuaries showing change in shoreline mangrove cover 1989 to 2015

14°42'0"S

Legend

144°6'0"E

144°12'0"E

Marrett River

Normanby River

14°24'0"S

Estuary Shoreline Change Normanby & Marrett Rivers 1989 to 2015

144°9'0"E

14°33'0"S

14°30'0"S

14°27'0"S

Princess Charlotte Bay

Pg No

Legend

Shoreline Change Stable Mangrove Mangrove Loss 0

0.5

1

2

3

Kilometers 4

Map of Normanby & Marrett estuaries showing change in shoreline mangrove cover 1989 to 2015

14°36'0"S

Mangrove Gain


Results Along PCB estuary shoreline there has been an overall increase in mangrove cover of 12% since 1989. Patterns of mangrove expansion and loss within the estuary are similar for the Bizant and Normanby, but different in the Kennedy and Marratt systems. In the Bizant and Normanby Rivers, there has been a net loss of mangroves in the lower estuary with increasing mangrove expansion upstream. In the Kennedy River, infilling of an ox-bow has resulted in a large (50%) increase in mangrove cover in the lower estuary. Mangrove expansion is occurring in upstream reaches. Unlike other estuaries, there is more erosion and net loss of mangrove cover within the mid Kennedy estuary. In the Marratt estuary, there was a net increase in mangrove cover in the lower estuary, compared to the Normanby and Bizant systems. Similar to other estuaries mangrove expansion is occurring the upper estuary. Discussion There is more mangrove expansion relative to mangrove loss in all upstream reaches of PCB estuaries. Similarly, mangrove loss to gain ratios are highest in the lower estuary for all estuaries except the Kennedy River estuary. The patterns of mangrove loss and expansion within the Normanby and Bizant systems follows patterns that would be anticipated to occur under sea level rise scenarios, with mangrove expansion in the upper estuary and net mangrove loss in the lower estuary. In the Kennedy River system, patterns of estuary process are Figure 26 Mangrove infilling is occurring in the Kennedy masked by infilling of an ox River along a remnant river ox-bow bow. Further analysis is required to exclude this effect from process within the main Kennedy River estuary. Of interest is the net loss of mangrove cover in the mid Kennedy River estuary. This observation follows similar observations of shoreline erosion from shoreline video assessment in the estuary in 2014. Increased erosion within mid-estuaries is often associated with a decrease in coarse sediment supply, usually linked to altered hydrology within the lower catchment. It is not clear what may be driving this process in the Kennedy River. The Marratt River has also experienced a much greater increase in mangrove cover along estuary margins compared to the Normanby and Bizant systems, with net mangrove gains present in all estuary sections. There has also been less overall loss

48


% Change in estuary shoreline mangrove extent

of mangrove extent within the Marratt system. The mangrove loss to gain ratio for the upper estuary is slightly higher compared with other estuaries. These observations may indicate that the Marratt River is more hydrologically stable compared to other systems, with lower flow and less intense high flow events. Additionally these observations may also indicate greater sediment trapping capacity within the Marratt estuary system which facilitates mangrove expansion and reduces estuary shoreline erosion. In the upper estuary, anthropogenic disturbance associated with camp grounds, boat launches and cattle grazing may be exacerbating estuary shoreline retreat and preventing mangrove colonisation. Visual inspection of mangrove change along the Marratt River estuary (Figure 29) shows areas of erosion in close proximity to areas with increased human and cattle presence. These areas provide focal points for on-ground action to reduce human and cattle impacts to estuary shorelines that are increasing erosion and consequently increasing sediment export to PCB and the northern Great Barrier Reef. 70

Change in estuary shoreline mangrove extent within Princess Charlotte Bay

60 50 40

Mangrove Loss

30

Mangrove Gain

20 10 0 -10

-20 Lower Mid Upper Lower Mid Upper Lower Mid Upper Lower Mid Upper -30 Kennedy

Bizant

Normanby

Marratt

Total

Estuary Shoreline Figure 28 Graph showing change in estuary shoreline mangrove extent

Estuary Mangrove Loss to Gain Ratio

Loss to Gain Ratio

2.5 2 1.5 1 0.5 0 Lower Mid UpperLower Mid UpperLower Mid UpperLower Mid Upper Kennedy

Bizant

Normanby

Marrett

Total

Figure 27 Estuary shoreline mangrove loss to gain ratio

49

` Improving climate change resilience and reducing sediment runoff through better mangrove management – TropWATER July 2016 144°12'0"E

14°33'0"S

¯

14°36'0"S

Pg No

0

0.225 0.45

0.9

1.35

Kilometers 1.8

Map of Normanby & Marrett estuaries showing change in shoreline mangrove cover 1989 to 2015

Figure 29 Anthropogenic vehicle and cattle impacts ay exacerbate erosion along the upper Marratt River estuary

50


Case Study 4: Upland Migration and Terrestrial Retreat

Figure 30 Sea level rise indicator 4: Upland mangrove migration and terrestrial retreat

Achievements 2015 1. Assessment of terrestrial vegetation condition at the tidal-terrestrial interface in the East Normanby focal study area from 726 images collected during aerial helicopter surveys in 2014 undertaken with Kalpowar Rangers. 2. Mapped 2014 terrestrial-tidal interface vegetation condition along 37 km of edge. 3. Mapped historical and recent change in vegetation cover at the terrestrial-tidal interface between 1989 and 2015 from Landsat imagery. 4. Mapped historical and recent trends in vegetation condition at the terrestrialtidal interface between 1989 and 2015 from Landsat imagery. 5. Established 10 permanent transects at the terrestrial-tidal margin to assess vegetation shifts and ground-truth satellite image assessment. Data was collected with Kalpowar Rangers during the 2015 field season. 6. Measured sediment conditions at the terrestrial-tidal margin along permanent transects to assess effects of vehicle and cattle disturbance on sediment conditions with implications for tidal and terrestrial interface vegetation resilience. 7. Compiled a list of tidal wetland species present at the terrestrial interface. 8. Tagged and measured 81 mangrove seedlings present near HAT at 5 locations to assess viability and recruitment success as an indicator of mangrove upland migration. These will be re-measured in 2016.

51


Key Findings Aerial Surveys 1. 51% of terrestrial tree stands along the tidal margin are experiencing dieback. 32% of this terrestrial margin has some or many dead trees present, with 13% showing signs of extensive terrestrial retreat. There was vey little new growth (