Soils of part of Matakarapa Island Foxton

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1 Soils of part of Matakarapa Island Foxton

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3 Malcolm McLeod Prepared for: Lowe Environmental Impact 441 Church Street, Palmerston North PO Box 4667 Palmerston North 4442 New Zealand April 2015, Gate 10 Silverdale Road, University of Waikato Campus, Private Bag 3127, Hamilton 3240, New Zealand, Ph , Fax ,

4 Reviewed by: Approved for release by: Jackie Aislabie Scientist Sam Carrick Research Priority Leader Characterising Land Resources Contract Report: LC 2197 Disclaimer This report has been prepared by for Lowe Environmental Impact. If used by other parties, no warranty or representation is given as to its accuracy and no liability is accepted for loss or damage arising directly or indirectly from reliance on the information in it. New Zealand Ltd and Lowe Environmental Impact 2015 No part of this work covered by copyright may be reproduced or copied in any form or by any means (graphic, electronic, digital or mechanical, including photocopying, recording, taping, information retrieval systems, or otherwise), in whole or in part, without the written permission of or Lowe Environmental Impact.

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7 Contents Summary... v 1 Introduction Objectives Methods Results and discussion Conclusions References Appendix 1 Soil profile descriptions Appendix 2 Maps Page iii

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9 Summary Project and Client Horowhenua District Council through Lowe Environmental Impact contracted to map soils on the southern part Matakarapa Island, Foxton, as part of the HDC process to gain consent to discharge treated municipal effluent to land on Matakarapa Island. Objectives Map and describe morphological properties of soils on part of Matakarapa Island, Foxton, with emphasis on: Physical soil property descriptions of 1-m deep soil profiles including colour, texture, structure, cohesion, drainage class, porosity, depth to restrictive layer, hydrophobicity, water-holding capacity, and preferred drainage pathways Terrain mapping for slope and elevation Erosion susceptibility Observations of plant species and vitality as indicators of soil nutrient and moisture conditions Hydrology and hydrogeology mapping and descriptions, including surface drains, ponding, pugging, and spring mapping. Methods Standard soil survey methods were employed following Milne et al. (1995), with slopes generated off LiDAR data supplied by the client. Results and conclusions The study area on the southern part of Matakarapa Island, Foxton, occupies about 60% of the island. Soils developed in sand dunes are generally well drained whereas soils developed in inter-dune and sand plain areas are generally moderately well drained. Poorly drained soils occur on the sand plains where clayey alluvium from the former Manawatu River or Moutua flood protection scheme has over-ridden the sand plain and blocked drainage or proximity to the former Manawatu River has caused a high water table. Generally, the well and moderately well drained sandy soils do not have hydraulically restrictive layers within 1 m of the soil surface. They show signs of hydrophobicity. Similar soils held in the National Soils Database (NSD) have approximately 155 mm total available water to 1 m depth, with approximately 95 mm of that being readily available to plants. Page v

10 Most slopes are less than 15 with the majority being 0 3. In keeping with a sand dune landscape, there is much natural and human induced soil erosion/accumulation in the study area. Much of the sand plain and inter-dune land has been affected by smoothing cultivation to pasture. Marram grass native trees (mānuka) and exotic scrub (gorse, lupin, and boxthorn) occur on the dunes. Low fertility pasture with lupin occurs on upper sand plain terraces, while improved pasture occurs on lower sand plain terraces. Rushes and water pepper occur on sand plain pastures where the soil is imperfectly or poorly drained. Wetland vegetation occurs in a former lagoon. Artificial drains are largely confined to the south-eastern low-lying area. Areas of surface pugging are largely confined to poorly and imperfectly drained soils on the sand plain. Page vi

11 1 Introduction Horowhenua District Council (HDC), through Lowe Environmental Impact (LEI), contracted to map soils on the southern part of Matakarapa Island, Foxton, as part of the HDC process to gain consent to discharge treated municipal effluent to land on part of Matakarapa Island. 2 Objectives Map and describe morphological properties of soils on the southern part of Matakarapa Island, Foxton (location of study area Figure 7), with emphasis on: Physical soil property descriptions of 1-m deep soil profiles including colour, texture, structure, cohesion, drainage class, porosity, depth to restrictive layer, hydrophobicity, water-holding capacity, and preferred drainage pathways Terrain mapping for slope and elevation Erosion susceptibility Observations of plant species and vitality as indicators of soil nutrient and moisture conditions Hydrology and hydrogeology mapping and descriptions, including surface drains, ponding, pugging, and spring mapping. 3 Methods Geomorphic position follows Milne et al. (1995) where a dune is a low mound, ridge, bank, or hill of loose granular material generally sand, either bare or covered with vegetation, capable of movement from place to place but always retaining its overall shape. An interdune area is the relatively flat surface between dunes. At Matakarapa Island the inter-dune areas are not wide and they may often be hollows. A sand plain is the sand-covered plain between sand dunes. To determine soil drainage class the following criteria were used (Table 1). Table 1 Abbreviated definition of drainage classes (after Milne et al. 1995) Drainage class Poorly drained Imperfectly drained Moderately well drained Well drained Definition Grey mottle colours <30 cm from soil surface Grey mottle colours >30 <60 cm from soil surface Ochreous mottles >30 or grey mottles >60 cm No mottles within 1 m Page 1

12 Free traverse was used to determine the location of soil-inspection hand-auger holes. Auger holes were located by hand-held GPS. At each auger hole location a cm pit was dug to about 40 cm and a 6-cm diameter hand auger used to collect soil morphological information down to 1 m. Soil colour, including mottling, texture, and the presence or absence of hydraulically limiting soil layers was noted. Soil colour was used as a guide both to drainage class (Table 1) and to the presence of a water table noted if present while the auger hole was open. Slope classes (Lynn et al. 2009) were generated from LiDAR data supplied by the client and clipped to the study area. Contour elevation data was supplied by the client and a world file written to allow it to be used in the GIS. For completeness, the photo has been clipped to the boundaries of the study area. Erosion susceptibility has been judged in the field by direct observation and follows Milne et al. (1995). The location of artificial drains was determined in the field and also by using the clientsupplied LiDAR data. Total porosity and water storage values were extracted from the National Soils Database. Chemical analyses were based on those presented in Cowie et al. (1967). 4 Results and discussion Matakarapa Island is formed by the current path of the Manawatu River having cut off a large loop in the river. A hill shade map generated from the LiDAR data, and used as the base for maps, highlights a pre-existing river channel, now largely covered by sand from dune blowouts, within the island. The study area on the southern part of Matakarapa Island, Foxton, occupies about 60% of the island. Sand dunes (Figure 8) make up ca 44% of the mapped area excluding ponds, while interdunes, sand plains and alluvium over sand make up ca 13%, 30%, and 9% respectively (Table 2). Table 2 Physiographic units identified, area and % of study area Physiographic unit Area (ha) % of area Sand dune Inter dune Sand plain Alluvium over sand In excess of 70 soil observations were made to a depth of 1 m. The sandy soils have very weak or weak soil strength with single grain soil structure. Where clayey alluvium occurs on the low-lying ground (alluvium over sand physiographic unit), soil strength is weak or Page 2

13 slightly firm, soil structure is moderately pedal with very fine and fine polyhedral peds. In some older cuttings the sandy soil appeared to be firmer, possibly from exposure to sodiumrich, salt-laden air. Fresh pits dug back from the cuttings did not contain the firmer layers. Soil observations show that the sand dunes are generally well drained without mottles in the top 1 m, whereas inter-dune and sand plain areas contain moderately well drained soils with ochreous (rust coloured) mottles at less than 90 cm from the soil surface (Figure 1). Ochreous mottles indicate oxygen-poor conditions for part of the year, generally caused by waterlogging of the soil. Unlike many hilly areas in less sandy soil parent materials, the sand dune soils are not less well drained in foot slope areas. Areas of the different drainage classes are given in Table 3 and their spatial distribution shown in Figure 9. Table 3 Soil drainage classes identified, area and % of study area Drainage class Area (ha) % of area Well drained Moderately drained Imperfectly drained Poorly drained <2 7 For this study, traditional geographic soil names have not been allocated to the soils because the study area has not been put in context of the dune building stages of Cowie et al. (1967). The classical three phase dune building stages may not exist at the study site. Seven soil classes have been identified based on physiographic position and drainage class. The soil classes are given in Table 4 as well as their provisional correlation with Cowie et al. (1967). Their distribution is shown in Figure 10. Typical soil descriptions are given in the Appendix. Table 4 Soil classes identified, area and % of study area Soil class Area (ha) % of area Provisional correlation* Dune, well drained Part Waitarere-Hokio Association Inter dune, moderately drained Part Waitarere-Hokio Association Sand plain, well drained 0.5 <1 Part Awahou-Foxton association Sand plain, moderately drained Part Awahou-Foxton association Alluvium over sand, moderately drained 2.8 <2 Part Meanee-Farndon series Alluvium over sand, imperfectly drained 2.7 <2 Part Meanee-Farndon series Alluvium over sand, poorly drained Part Meanee-Farndon series *Provisionally correlated with Cowie et al. (1967). Page 3

14 Figure 1 Ochreous mottles within the sandy soil profile indicate waterlogging for short periods of the year. The GPS used for scale is 16 cm high. Low-lying areas in the south east have received additions of clayey alluvium presumably from the Moutua flood diversion scheme and are poorly drained except in levee positions where they may be well drained. Total porosity and water-holding capacity of the soils have not been established as this requires laboratory measurements. However, the National Soils Database (NSD) shows the Foxton black sand, sampled near Te Horo approximately 40 km to the south west of the study site, has total porosity of 50 60% throughout the soil profile and approximately 155 mm total available water ( kpa) to 1 m depth with approximately 95 mm of that being readily available to plants kpa). The sampled soil had a thick topsoil where A and AB soil horizons totalled 40 cm thick. Thus the total and readily available water storage may be higher than in the study site where topsoils are thinner. The soil observations generally show no hydraulically restricting layers (e.g. iron pans) within a depth of 1 m. except for one observation where the iron pan was thin and likely spatially ephemeral. In two small inter-dune areas adjacent to the Manawatu River, slightly firmer loamy sand was encountered at 85 cm and 100 cm depth. The full spatial extent and hydraulic conductivity of these layers has not been investigated. Page 4

15 Many of the sandy soils in the study area appear to be hydrophobic judging from the irregular wetting patterns within the soil (Figure 2). Hydrophobicity will need to be considered when designing the effluent irrigation system. Figure 2 Irregular wetting of the topsoil and uppermost subsoil in a sand dune soil indicating hydrophobicity. Spade for scale is 90 cm high. Page 5

16 The majority of slopes are less than 15 (rolling) with most being 0 3 (flat to undulating) (Table 5) and are shown spatially in Figure 11. Table 5 Percent of each slope class within the study area Slope class ( ) Name of class Percent of area >35 Flat to undulating Undulating Rolling Strongly rolling Moderately steep Steep Very steep Contour elevation data as supplied by the client are likely derived from the Digital Elevation Model also supplied by the client. The contour map was supplied as hard copy for which a world file was written to use the map in the GIS and clipped to the study area boundary (Figure 11). Positional accuracy is likely to be low as pixel size in the world file was estimated from ground features. Maximum elevation is about 45 m a.s.l. in the sand dunes with sand plains about 3 8 m a.s.l. The alluvium over sand physiographic unit ranges from about 0.5 to 10 m a.s.l. Currently, the sand country in the study area is largely vegetated, which minimises wind erosion. However, the thin and over-thickened topsoils observed in many places indicate that wind erosion of the sandy soils has been common. The large, low-relief, oblate feature in the central study area is deposition from a dune blow out. In the east of the study area steep slopes rise from the Foxton River and are susceptible to wind erosion as well as under cutting from the Foxton River. In keeping with a sand dune landscape, there is modification of the landscape by soil erosion/accumulation both natural and human induced (Figure 3, Figure 4). Thus when distinguishing between soil profiles, less concern should be placed on the upper soil profile and more weight placed on drainage conditions in the sandy soils. While the sandy dune soils likely have relatively low organic carbon values in the topsoil, erosion/deposition will reduce the organic carbon values to even lower levels. Organic carbon is largely responsible for nutrient and water retention in these sandy soils (Table 6). Page 6

17 Figure 3 Modification of a sand dune. Figure 4 Modification of a sand plain. Artificial drains are largely confined to the south eastern low-lying area. An artificial channel drains the effluent ponds westward (Figure 12). Natural vegetation may reflect soil conditions in an undisturbed setting but in a farmed setting may reflect management (Figure 5). Figure 5 Juncus spp. with pasture grass on the left of the fence but not on the right indicates vegetation can be affected by management. Much of the study area is farmed but in places some indication of soil conditions is shown in the vegetation. Marram grass native trees (mānuka) and exotic scrub (gorse, lupin, and boxthorn) occur on the dunes. Pasture vegetation does vary with the dune building phase as indicated by a change in terrace height at about 5 m above sea level. This study does not identify whether or not the vegetation change is based on management. Low fertility pasture with lupin occurs on upper sand plain terraces while improved pasture occurs on lower sand plain terraces. Low-lying pasture areas that are wet have rushes (Juncus spp.) and/or water pepper (Polygonum hydropiper) in the pasture and surface pugging due to stock treading. Very wet areas have wetland vegetation, and surface water, and are not used intensively for grazing. Page 7

18 Areas of surface pugging are largely confined to low-lying poorly and imperfectly drained soils on the sand plain. An inter-dune lake lies to the south of the treatment ponds (Figure 6) but does not appear on NZMS 1 4 th edition (1974), or the more recent digital version of the 1: scale NZTM maps, indicating it may be a transient feature or induced by the effluent pond system. The 1967 soil map (Cowie et al. 1967) shows a lagoon to the south west of the current treatment ponds but the lagoon is not shown on NZMS 1 4 th edition (1974). Today the lagoon is intersected by a surface drain and may empty in summer, although wetland vegetation persists. Figure 6 An inter-dune lake occurring south of the treatment ponds. Other enclosed basins within the dune system could be used for storage of effluent if lined with an impermeable membrane. Chemical analyses have not been made from soils at this site. However, Cowie et al. (1967) present the following chemical data (Table 6) for Waitarere and Awahou soils, which have been interpreted as a soil from the dune and from the sand plain respectively. Page 8

19 Table 6 Soil chemical data for a similar soil located on a dune and one on the sand plain after Cowie et al. (1967) Soil Depth (in) ph Organic carbon (%) Total N (%) CEC cmol c kg -1 soil Vegetation Dune sand Maram grass Sand plain Low producing pasture The data show that the dune sand soil sampled by Cowie et al. (1967) has a thin topsoil with low organic carbon, total nitrogen, CEC, and very low values in the subsoil. ph is high because of the presence of CaCO 3 (values not shown). Low CEC values reflect the sandy nature of the soil. In contrast, the soil sampled by Cowie et al. (1967) on the sand plain has a thicker topsoil and a higher value of organic carbon which in turn leads to higher total nitrogen and CEC values. These soils, sampled by Cowie et al. (1967), represent single locations only and much variation can be expected. However, low organic carbon, total nitrogen, and CEC can be expected over much of the study area in the sandy soils. 5 Conclusions The study area on the southern part of Matarakarapa Island, Foxton occupies about 60% of the island. The sandy soils have very weak or weak soil strength with single grain soil structure; however, where clayey alluvium occurs on the low-lying ground soil strength is weak or slightly firm, moderately pedal with very fine and fine polyhedral peds. The sand dunes are generally well drained without mottles in the top 1 m, whereas inter-dune and sand plain areas contain moderately well drained. The sand dune soils do not become less well drained in foot slope areas. Low-lying areas in the south east are poorly drained except in levee positions where they may be well drained. Data from similar soils in the NSD have total porosity of 50 60% throughout the soil profile and approximately 155 mm total available water to 1 m depth with approximately 95 mm of that being readily available to plants. The soil observations generally show no hydraulically restricting layers (e.g. iron pans) within a depth of 1 m. Many of the sandy soils in the study area appear to be hydrophobic. Most slopes are less than 15, with the majority being 0 3. In keeping with a sand dune landscape, there is much soil erosion/accumulation in the study area. Much of the inter-dune land has been affected by smoothing cultivation to pasture. Page 9

20 Marram grass native trees (mānuka) and exotic scrub (gorse, lupin, and boxthorn) occur on the dunes. Low fertility pasture with lupin occurs on upper sand plain terraces while improved pasture occurs on lower sand plain terraces. Low-lying areas on the sand plain with poorly drained soils have a pugged surface whose vegetation includes rushes and water pepper. Wetland vegetation occurs in a former lagoon. An inter-dune lake lies to the south of the treatment ponds and a lagoon to the south west of the current treatment ponds is intersected by a surface drain and may empty in summer, although wetland vegetation persists. Artificial drains are largely confined to the south eastern low-lying area. Areas of surface pugging are largely confined to low-lying, poorly and imperfectly drained soils on the sand plain. 6 References Cowie JD, Fitzgerald P, Owers W Soils of the Manawatu-Rangitikei Sand Country. New Zealand Soil Bureau Bulletin 29. Government Printer, Wellington, New Zealand. Lynn IH, Manderson AK, Page MJ, Harmsworth GR, Eyles GO, Douglass GB, Mackay AD, Newsome PJF Land Use Capability Survey Handbook a New Zealand handbook for the classification of land. 3 rd edn. Hamilton, Agresearch; Lincoln, ; Lower Hutt, GNS Science. 163p. Milne JDG, Clayden B, Singleton PL, Wilson AD Soil description handbook. Rev.edn. Manaaki Whenua Press, Lincoln, New Zealand. Page 10

21 Appendix 1 Soil profile descriptions A typical well-drained soil in the sand dunes on a 34 shoulder slope is: Ap 0 17 cm Dark brown (10YR 3/3) sand; very friable; single grain structure; distinct wavy boundary. Bw cm Olive brown (2.5Y 4/3) sand; very friable; single grain structure; diffuse boundary. C cm Dark greyish brown (2.5Y 4/2) sand; very friable; single grain structure Note. On many slopes the topsoil is thinner or absent. A typical moderately drained soil in the inter dunes on a gently undulating slope is: Ap 0 12 cm Very dark greyish brown (10YR 3/2) sand; very friable; single grain structure; distinct wavy boundary. Bw cm Olive brown (2.5Y 4/4) sand; very friable; single grain structure; diffuse boundary. Bw cm Olive brown (2.5Y 4/3) sand; very friable; single grain structure; indistinct boundary. C(f) cm Dark greyish brown (2.5Y 4/2) sand; many medium faint yellowish brown (10YR 5/6) mottles; very friable; single grain structure; indistinct boundary. A well-drained soil on the sand plain is: Ap 0 25 cm Black (10YR 2/1) sand; very friable; single grain structure; indistinct boundary. bap cm Dark yellowish brown (10YR 3/4) sand; very friable; single grain structure; diffuse boundary. Bw cm Olive brown (2.5Y 4/4) sand; very friable; single grain structure; diffuse boundary. C cm Olive brown (2.5Y 4/3) sand; very friable; single grain structure indistinct boundary. Note this soil has an over thickened topsoil as a result of accumulation or cultivation. A typical moderately drained soil on the sand plain is: Ap 0 20 cm Black (10 YR3/1) sand; very friable; single grain structure; distinct wavy boundary. Page 11

22 Bw cm Brown (2.5Y 5/3) sand; very friable; single grain structure; diffuse boundary. Bw(f) cm Brown (2.5Y 5/3) sand; many medium faint yellowish brown (10YR 5/6) mottles; very friable; single grain structure; indistinct boundary. C(f) cm Very moist; dark grey (2.5Y 4/0) sand; few medium faint yellowish brown (10YR 5/6) mottles; very friable; single grain structure. A typical moderately drained soil on a flat surface developed in alluvium over sand is: Ap 0 40 cm Greyish brown (10YR5/2) silt loam; slightly sticky; abundant very fine polyhedral peds; distinct wavy boundary. Bw(f) cm Olive brown (2.5Y 4/3) sand; many medium distinct yellowish brown (10YR 5/6) mottles; very friable; single grain structure; diffuse boundary. C(f) cm Dark grey (2.5Y 4/1) sand; many medium distinct yellowish brown (10YR 5/6) mottles; very friable; single grain structure. A typical imperfectly drained soil on a flat surface developed in alluvium over sand is: Ap 0 7 cm Very dark greyish brown (10YR 3/2) silty clay; slightly sticky; abundant very fine polyhedral peds; distinct wavy boundary. Bw(f) 7 90 cm Dark grey (2.5Y 4/1) silty clay; many medium distinct strong brown brown (7.5YR 4/6) mottles; very friable; single grain structure; diffuse boundary. C(f) cm Dark grey (2.5Y 4/1) sand; many medium distinct yellowish brown (10YR 5/6) mottles; very friable; single grain structure. A typical poorly drained soil on a flat surface developed in alluvium over sand is: Ap 0 33 cm Dark grey (2.5Y 4/0) silty clay; many fine distinct grey (10YR 5/1) mottles; slightly sticky; abundant very fine polyhedral peds; distinct wavy boundary. Br cm Dark grey (2.5Y 4/1) sand; many medium distinct yellowish brown brown (10YR 5/6) mottles; very friable; single grain structure; diffuse boundary. Cr cm Dark grey (2.5Y 4/1) sand; many medium distinct strong brown (7.5YR 5/6) mottles; very friable; single grain structure. Page 12

23 Appendix 2 Maps Figure 7 Location of study area on Matakarapa Island, Foxton. Page 13

24 Figure 8 Map of physiographic units on Matakarapa Island, Foxton. Page 14

25 Figure 9 Soil distribution on Matakarapa Island, Foxton. Page 15

26 Figure 10 Slope class distribution on Matarakapa Island, Foxton. Page 16

27 Figure 11 Elevation and contour data for Matakarapa Island, Foxton. Page 17

28 Figure 12 Location of artificial drainage channels on Matakarapa Island, Foxton. Page 18